diff --git a/mps/code/mpm.h b/mps/code/mpm.h
index ebe75a09707..17ece35d524 100644
--- a/mps/code/mpm.h
+++ b/mps/code/mpm.h
@@ -475,7 +475,7 @@ extern double TraceWorkFactor;
 
 extern Res TraceScanArea(ScanState ss, Word *base, Word *limit,
                          mps_area_scan_t scan_area,
-                         void *closure, size_t closure_size);
+                         void *closure);
 extern void TraceScanSingleRef(TraceSet ts, Rank rank, Arena arena,
                                Seg seg, Ref *refIO);
 
@@ -966,7 +966,7 @@ extern Res RootCreateArea(Root *rootReturn, Arena arena,
                           Rank rank, RootMode mode,
                           Word *base, Word *limit,
                           mps_area_scan_t scan_area,
-                          void *closure, size_t closure_size);
+                          void *closure);
 extern Res RootCreateAreaTagged(Root *rootReturn, Arena arena,
                                 Rank rank, RootMode mode,
                                 Word *base, Word *limit,
@@ -975,7 +975,7 @@ extern Res RootCreateAreaTagged(Root *rootReturn, Arena arena,
 extern Res RootCreateThread(Root *rootReturn, Arena arena,
                             Rank rank, Thread thread,
                             mps_area_scan_t scan_area,
-                            void *closure, size_t closure_size,
+                            void *closure,
                             Word *stackCold);
 extern Res RootCreateThreadTagged(Root *rootReturn, Arena arena,
                                   Rank rank, Thread thread,
diff --git a/mps/code/mps.h b/mps/code/mps.h
index 737677da518..65ab6d6bbf3 100644
--- a/mps/code/mps.h
+++ b/mps/code/mps.h
@@ -109,8 +109,7 @@ typedef struct mps_scan_tag_s {
 } mps_scan_tag_s;
 
 typedef mps_res_t (*mps_root_scan_t)(mps_ss_t, void *, size_t);
-typedef mps_res_t (*mps_area_scan_t)(mps_ss_t, void *, void *,
-                                     void *, size_t);
+typedef mps_res_t (*mps_area_scan_t)(mps_ss_t, void *, void *, void *);
 typedef mps_res_t (*mps_fmt_scan_t)(mps_ss_t, mps_addr_t, mps_addr_t);
 typedef mps_res_t (*mps_reg_scan_t)(mps_ss_t, mps_thr_t,
                                     void *, size_t);
@@ -682,7 +681,7 @@ extern mps_res_t mps_root_create_table_masked(mps_root_t *, mps_arena_t,
 extern mps_res_t mps_root_create_area(mps_root_t *, mps_arena_t,
                                       mps_rank_t, mps_rm_t,
                                       void *, void *,
-                                      mps_area_scan_t, void *, size_t);
+                                      mps_area_scan_t, void *);
 extern mps_res_t mps_root_create_area_tagged(mps_root_t *, mps_arena_t,
                                              mps_rank_t, mps_rm_t,
                                              void *, void *,
@@ -700,7 +699,7 @@ extern mps_res_t mps_root_create_thread(mps_root_t *, mps_arena_t,
 extern mps_res_t mps_root_create_thread_scanned(mps_root_t *, mps_arena_t,
                                                 mps_rank_t, mps_rm_t, mps_thr_t,
                                                 mps_area_scan_t,
-                                                void *, size_t,
+                                                void *,
                                                 void *);
 extern mps_res_t mps_root_create_thread_tagged(mps_root_t *, mps_arena_t,
                                                mps_rank_t, mps_rm_t, mps_thr_t,
@@ -820,18 +819,10 @@ extern void mps_pool_check_free_space(mps_pool_t);
 
 /* Scanner Support */
 
-extern mps_res_t mps_scan_area(mps_ss_t,
-                               void *, void *,
-                               void *, size_t);
-extern mps_res_t mps_scan_area_masked(mps_ss_t,
-                                      void *, void *,
-                                      void *, size_t);
-extern mps_res_t mps_scan_area_tagged(mps_ss_t,
-                                      void *, void *,
-                                      void *, size_t);
-extern mps_res_t mps_scan_area_tagged_or_zero(mps_ss_t,
-                                              void *, void *,
-                                              void *, size_t);
+extern mps_res_t mps_scan_area(mps_ss_t, void *, void *, void *);
+extern mps_res_t mps_scan_area_masked(mps_ss_t, void *, void *, void *);
+extern mps_res_t mps_scan_area_tagged(mps_ss_t, void *, void *, void *);
+extern mps_res_t mps_scan_area_tagged_or_zero(mps_ss_t, void *, void *, void *);
 
 extern mps_res_t mps_fix(mps_ss_t, mps_addr_t *);
 
diff --git a/mps/code/mpsi.c b/mps/code/mpsi.c
index 655a226549c..c9acee2da5e 100644
--- a/mps/code/mpsi.c
+++ b/mps/code/mpsi.c
@@ -1302,7 +1302,7 @@ mps_res_t mps_root_create_table(mps_root_t *mps_root_o, mps_arena_t arena,
 
   res = RootCreateArea(&root, arena, rank, mode,
                        (void *)base, (void *)(base + size),
-                       mps_scan_area, NULL, 0);
+                       mps_scan_area, NULL);
 
   ArenaLeave(arena);
 
@@ -1317,7 +1317,7 @@ mps_res_t mps_root_create_area(mps_root_t *mps_root_o,
                                mps_rank_t mps_rank, mps_rm_t mps_rm,
                                void *base, void *limit,
                                mps_area_scan_t scan_area,
-                               void *closure, size_t closure_size)
+                               void *closure)
 {
   Rank rank = (Rank)mps_rank;
   Root root;
@@ -1335,7 +1335,7 @@ mps_res_t mps_root_create_area(mps_root_t *mps_root_o,
 
   res = RootCreateArea(&root, arena, rank, mode,
                        base, limit,
-                       scan_area, closure, closure_size);
+                       scan_area, closure);
 
   ArenaLeave(arena);
 
@@ -1478,7 +1478,6 @@ mps_res_t mps_root_create_thread_scanned(mps_root_t *mps_root_o,
                                          mps_thr_t thread,
                                          mps_area_scan_t scan_area,
                                          void *closure,
-                                         size_t closure_size,
                                          void *cold)
 {
   Rank rank = (Rank)mps_rank;
@@ -1497,7 +1496,7 @@ mps_res_t mps_root_create_thread_scanned(mps_root_t *mps_root_o,
 
   /* See .root-mode. */
   res = RootCreateThread(&root, arena, rank, thread,
-                         scan_area, closure, closure_size,
+                         scan_area, closure,
                          (Word *)cold);
 
   ArenaLeave(arena);
diff --git a/mps/code/prmci3fr.c b/mps/code/prmci3fr.c
index d9f989db17c..87ec5f436dc 100644
--- a/mps/code/prmci3fr.c
+++ b/mps/code/prmci3fr.c
@@ -40,7 +40,7 @@ Addr MutatorFaultContextSP(MutatorFaultContext mfc)
 
 Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
                             mps_area_scan_t scan_area,
-                            void *closure, size_t closure_size)
+                            void *closure)
 {
   Res res;
 
@@ -51,7 +51,7 @@ Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
     ss,
     (Word *)mfc->ucontext,
     (Word *)((char *)mfc->ucontext + sizeof(*(mfc->ucontext))),
-    scan_area, closure, closure_size
+    scan_area, closure
   );
 
   return res;
diff --git a/mps/code/prmci3li.c b/mps/code/prmci3li.c
index 419f83f8b4a..da04ac4810b 100644
--- a/mps/code/prmci3li.c
+++ b/mps/code/prmci3li.c
@@ -103,7 +103,7 @@ Addr MutatorFaultContextSP(MutatorFaultContext mfc)
 
 Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
                             mps_area_scan_t scan_area,
-                            void *closure, size_t closure_size)
+                            void *closure)
 {
   mcontext_t *mc;
   Res res;
@@ -115,7 +115,7 @@ Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
   res = TraceScanArea(ss,
                       (Word *)mc,
                       (Word *)((char *)mc + sizeof(*mc)),
-                      scan_area, closure, closure_size);
+                      scan_area, closure);
   return res;
 }
 
diff --git a/mps/code/prmci3xc.c b/mps/code/prmci3xc.c
index abeef4988c4..8eda902c244 100644
--- a/mps/code/prmci3xc.c
+++ b/mps/code/prmci3xc.c
@@ -98,7 +98,7 @@ Addr MutatorFaultContextSP(MutatorFaultContext mfc)
 
 Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
                             mps_area_scan_t scan_area,
-                            void *closure, size_t closure_size)
+                            void *closure)
 {
   x86_thread_state32_t *mc;
   Res res;
@@ -110,7 +110,7 @@ Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
   res = TraceScanArea(ss,
                       (Word *)mc,
                       (Word *)((char *)mc + sizeof(*mc)),
-                      scan_area, closure, closure_size);
+                      scan_area, closure);
   return res;
 }
 
diff --git a/mps/code/prmci6fr.c b/mps/code/prmci6fr.c
index d8676d2a4c3..b1c1a67590f 100644
--- a/mps/code/prmci6fr.c
+++ b/mps/code/prmci6fr.c
@@ -34,7 +34,7 @@ Addr MutatorFaultContextSP(MutatorFaultContext mfc)
 
 Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
                             mps_area_scan_t scan_area,
-                            void *closure, size_t closure_size)
+                            void *closure)
 {
   Res res;
 
@@ -45,7 +45,7 @@ Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
     ss,
     (Word *)mfc->ucontext,
     (Word *)((char *)mfc->ucontext + sizeof(*(mfc->ucontext))),
-    scan_area, closure, closure_size
+    scan_area, closure
   );
 
   return res;
diff --git a/mps/code/prmci6li.c b/mps/code/prmci6li.c
index fe7cb96627a..67354c99414 100644
--- a/mps/code/prmci6li.c
+++ b/mps/code/prmci6li.c
@@ -107,7 +107,7 @@ Addr MutatorFaultContextSP(MutatorFaultContext mfc)
 
 Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
                             mps_area_scan_t scan_area,
-                            void *closure, size_t closure_size)
+                            void *closure)
 {
   mcontext_t *mc;
   Res res;
@@ -119,7 +119,7 @@ Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
   res = TraceScanArea(ss,
                       (Word *)mc,
                       (Word *)((char *)mc + sizeof(*mc)),
-                      scan_area, closure, closure_size);
+                      scan_area, closure);
   return res;
 }
 
diff --git a/mps/code/prmci6xc.c b/mps/code/prmci6xc.c
index 69591a321ab..ae8ef06f739 100644
--- a/mps/code/prmci6xc.c
+++ b/mps/code/prmci6xc.c
@@ -101,7 +101,7 @@ Addr MutatorFaultContextSP(MutatorFaultContext mfc)
 
 Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
                             mps_area_scan_t scan_area,
-                            void *closure, size_t closure_size)
+                            void *closure)
 {
   x86_thread_state64_t *mc;
   Res res;
@@ -113,7 +113,7 @@ Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
   res = TraceScanArea(ss,
                       (Word *)mc,
                       (Word *)((char *)mc + sizeof(*mc)),
-                      scan_area, closure, closure_size);
+                      scan_area, closure);
   return res;
 }
 
diff --git a/mps/code/prot.h b/mps/code/prot.h
index c2ae9d20e69..f3104cb27b7 100644
--- a/mps/code/prot.h
+++ b/mps/code/prot.h
@@ -32,7 +32,7 @@ extern Res ProtStepInstruction(MutatorFaultContext context);
 extern Addr MutatorFaultContextSP(MutatorFaultContext mfc);
 extern Res MutatorFaultContextScan(ScanState ss, MutatorFaultContext mfc,
                                    mps_area_scan_t scan,
-                                   void *closure, size_t closure_size);
+                                   void *closure);
 
 
 #endif /* prot_h */
diff --git a/mps/code/root.c b/mps/code/root.c
index 82737e536b0..ae16e3dcd13 100644
--- a/mps/code/root.c
+++ b/mps/code/root.c
@@ -17,13 +17,8 @@ SRCID(root, "$Id$");
 
 #define RootSig         ((Sig)0x51960029) /* SIGnature ROOT */
 
-typedef struct ClosureStruct {
-  void *p;
-  size_t s;
-} ClosureStruct;
-
 typedef union AreaScanUnion {
-  ClosureStruct closure;
+  void *closure;
   mps_scan_tag_s tag;       /* tag for scanning */
 } AreaScanUnion;
 
@@ -44,7 +39,8 @@ typedef struct RootStruct {
   union RootUnion {
     struct {
       mps_root_scan_t scan;     /* the function which does the scanning */
-      ClosureStruct closure;    /* closure for scan function */
+      void *p;                  /* closure for scan function */
+      size_t s;                 /* closure for scan function */
     } fun;
     struct {
       Word *base;               /* beginning of area */
@@ -274,7 +270,7 @@ Res RootCreateArea(Root *rootReturn, Arena arena,
                    Rank rank, RootMode mode,
                    Word *base, Word *limit,
                    mps_area_scan_t scan_area,
-                   void *closure, size_t closure_size)
+                   void *closure)
 {
   Res res;
   union RootUnion theUnion;
@@ -292,8 +288,7 @@ Res RootCreateArea(Root *rootReturn, Arena arena,
   theUnion.area.base = base;
   theUnion.area.limit = limit;
   theUnion.area.scan_area = scan_area;
-  theUnion.area.the.closure.p = closure;
-  theUnion.area.the.closure.s = closure_size;
+  theUnion.area.the.closure = closure;
 
   res = rootCreateProtectable(rootReturn, arena, rank, mode,
                               RootAREA, (Addr)base, (Addr)limit, &theUnion);
@@ -327,7 +322,7 @@ Res RootCreateAreaTagged(Root *rootReturn, Arena arena,
 Res RootCreateThread(Root *rootReturn, Arena arena,
                      Rank rank, Thread thread,
                      mps_area_scan_t scan_area,
-                     void *closure, size_t closure_size,
+                     void *closure,
                      Word *stackCold)
 {
   union RootUnion theUnion;
@@ -342,8 +337,7 @@ Res RootCreateThread(Root *rootReturn, Arena arena,
 
   theUnion.thread.thread = thread;
   theUnion.thread.scan_area = scan_area;
-  theUnion.thread.the.closure.p = closure;
-  theUnion.thread.the.closure.s = closure_size;
+  theUnion.thread.the.closure = closure;
   theUnion.thread.stackCold = stackCold;
 
   return rootCreate(rootReturn, arena, rank, (RootMode)0, RootTHREAD,
@@ -416,8 +410,8 @@ Res RootCreateFun(Root *rootReturn, Arena arena, Rank rank,
   AVER(FUNCHECK(scan));
 
   theUnion.fun.scan = scan;
-  theUnion.fun.closure.p = p;
-  theUnion.fun.closure.s = s;
+  theUnion.fun.p = p;
+  theUnion.fun.s = s;
 
   return rootCreate(rootReturn, arena, rank, (RootMode)0, RootFUN, &theUnion);
 }
@@ -535,8 +529,7 @@ Res RootScan(ScanState ss, Root root)
                         root->the.area.base,
                         root->the.area.limit,
                         root->the.area.scan_area,
-                        root->the.area.the.closure.p,
-                        root->the.area.the.closure.s);
+                        root->the.area.the.closure);
     if (res != ResOK)
       goto failScan;
     break;
@@ -546,16 +539,15 @@ Res RootScan(ScanState ss, Root root)
                         root->the.area.base,
                         root->the.area.limit,
                         root->the.area.scan_area,
-                        &root->the.area.the.tag,
-                        sizeof(root->the.area.the.tag));
+                        &root->the.area.the.tag);
     if (res != ResOK)
       goto failScan;
     break;
 
   case RootFUN:
     res = root->the.fun.scan(&ss->ss_s,
-                             root->the.fun.closure.p,
-                             root->the.fun.closure.s);
+                             root->the.fun.p,
+                             root->the.fun.s);
     if (res != ResOK)
       goto failScan;
     break;
@@ -564,8 +556,7 @@ Res RootScan(ScanState ss, Root root)
     res = ThreadScan(ss, root->the.thread.thread,
                      root->the.thread.stackCold,
                      root->the.thread.scan_area,
-                     root->the.thread.the.closure.p,
-                     root->the.thread.the.closure.s);
+                     root->the.thread.the.closure);
     if (res != ResOK)
       goto failScan;
     break;
@@ -574,8 +565,7 @@ Res RootScan(ScanState ss, Root root)
     res = ThreadScan(ss, root->the.thread.thread,
                      root->the.thread.stackCold,
                      root->the.thread.scan_area,
-                     &root->the.thread.the.tag,
-                     sizeof(root->the.thread.the.tag));
+                     &root->the.thread.the.tag);
     if (res != ResOK)
       goto failScan;
     break;
@@ -706,11 +696,10 @@ Res RootDescribe(Root root, mps_lib_FILE *stream, Count depth)
   switch(root->var) {
   case RootAREA:
     res = WriteF(stream, depth + 2,
-                 "area base $A limit $A scan_area closure $P closure_size $U\n",
+                 "area base $A limit $A scan_area closure $P\n",
                  (WriteFA)root->the.area.base,
                  (WriteFA)root->the.area.limit,
-                 (WriteFP)root->the.area.the.closure.p,
-                 (WriteFP)root->the.area.the.closure.s,
+                 (WriteFP)root->the.area.the.closure,
                  NULL);
     if (res != ResOK)
       return res;
@@ -732,8 +721,8 @@ Res RootDescribe(Root root, mps_lib_FILE *stream, Count depth)
     res = WriteF(stream, depth + 2,
                  "scan function $F\n", (WriteFF)root->the.fun.scan,
                  "environment p $P s $W\n",
-                 (WriteFP)root->the.fun.closure.p,
-                 (WriteFW)root->the.fun.closure.s,
+                 (WriteFP)root->the.fun.p,
+                 (WriteFW)root->the.fun.s,
                  NULL);
     if (res != ResOK)
       return res;
@@ -742,9 +731,8 @@ Res RootDescribe(Root root, mps_lib_FILE *stream, Count depth)
   case RootTHREAD:
     res = WriteF(stream, depth + 2,
                  "thread $P\n", (WriteFP)root->the.thread.thread,
-                 "closure $P size $U\n",
-                 (WriteFP)root->the.thread.the.closure.p,
-                 (WriteFU)root->the.thread.the.closure.s,
+                 "closure $P\n",
+                 (WriteFP)root->the.thread.the.closure,
                  "stackCold $P\n", (WriteFP)root->the.thread.stackCold,
                  NULL);
     if (res != ResOK)
diff --git a/mps/code/scan.c b/mps/code/scan.c
index 99b4d5d0987..3e01c9fed17 100644
--- a/mps/code/scan.c
+++ b/mps/code/scan.c
@@ -27,10 +27,9 @@
 
 mps_res_t mps_scan_area(mps_ss_t ss,
                         void *base, void *limit,
-                        void *closure, size_t closure_size)
+                        void *closure)
 {
   (void)closure; /* unused */
-  (void)closure_size; /* unused */
 
   MPS_SCAN_BEGIN(ss) {
     mps_word_t *p = base;
@@ -86,11 +85,10 @@ mps_res_t mps_scan_area(mps_ss_t ss,
 
 mps_res_t mps_scan_area_masked(mps_ss_t ss,
                                void *base, void *limit,
-                               void *closure, size_t closure_size)
+                               void *closure)
 {
   mps_scan_tag_t tag = closure;
   mps_word_t mask = tag->mask;
-  (void)closure_size; /* unused */
 
   MPS_SCAN_AREA_TAGGED(1);
 
@@ -109,12 +107,11 @@ mps_res_t mps_scan_area_masked(mps_ss_t ss,
 
 mps_res_t mps_scan_area_tagged(mps_ss_t ss,
                                void *base, void *limit,
-                               void *closure, size_t closure_size)
+                               void *closure)
 {
   mps_scan_tag_t tag = closure;
   mps_word_t mask = tag->mask;
   mps_word_t pattern = tag->pattern;
-  (void)closure_size; /* unused */
 
   MPS_SCAN_AREA_TAGGED(tag_bits == pattern);
 
@@ -139,12 +136,11 @@ mps_res_t mps_scan_area_tagged(mps_ss_t ss,
 
 mps_res_t mps_scan_area_tagged_or_zero(mps_ss_t ss,
                                        void *base, void *limit,
-                                       void *closure, size_t closure_size)
+                                       void *closure)
 {
   mps_scan_tag_t tag = closure;
   mps_word_t mask = tag->mask;
   mps_word_t pattern = tag->pattern;
-  (void)closure_size; /* unused */
 
   MPS_SCAN_AREA_TAGGED(tag_bits == 0 || tag_bits == pattern);
 
diff --git a/mps/code/ss.c b/mps/code/ss.c
index c0c109e01d2..fb23794c4a8 100644
--- a/mps/code/ss.c
+++ b/mps/code/ss.c
@@ -26,8 +26,7 @@ SRCID(ss, "$Id$");
 
 Res StackScanInner(ScanState ss, Word *stackCold, Word *stackHot,
                    Count nSavedRegs,
-                   mps_area_scan_t scan_area,
-                   void *closure, size_t closure_size)
+                   mps_area_scan_t scan_area, void *closure)
 {
   Arena arena;
   Res res;
@@ -50,16 +49,16 @@ Res StackScanInner(ScanState ss, Word *stackCold, Word *stackHot,
     AVER(stackHot < arena->stackAtArenaEnter);
     AVER(arena->stackAtArenaEnter < stackCold);
     res = TraceScanArea(ss, stackHot, stackHot + nSavedRegs,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if (res != ResOK)
       return res;
     res = TraceScanArea(ss, arena->stackAtArenaEnter, stackCold,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if (res != ResOK)
       return res;
   } else {
     res = TraceScanArea(ss, stackHot, stackCold,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if (res != ResOK)
       return res;
   }
diff --git a/mps/code/ss.h b/mps/code/ss.h
index 02dc34f9fcf..75d939194e2 100644
--- a/mps/code/ss.h
+++ b/mps/code/ss.h
@@ -33,11 +33,10 @@
  */
 
 extern Res StackScan(ScanState ss, Word *stackCold,
-                     mps_area_scan_t scan_area,
-                     void *closure, size_t closure_size);
+                     mps_area_scan_t scan_area, void *closure);
 extern Res StackScanInner(ScanState ss, Word *stackCold, Word *stackHot,
-                          Count nSavedRegs, mps_area_scan_t scan_area,
-                          void *closure, size_t closure_size);
+                          Count nSavedRegs,
+			  mps_area_scan_t scan_area, void *closure);
 
 #endif /* ss_h */
 
diff --git a/mps/code/ssan.c b/mps/code/ssan.c
index cbb0daa4dd2..2a36f493351 100644
--- a/mps/code/ssan.c
+++ b/mps/code/ssan.c
@@ -23,7 +23,7 @@ SRCID(ssan, "$Id$");
 
 Res StackScan(ScanState ss, Word *stackCold,
               mps_area_scan_t scan_area,
-              void *closure, size_t closure_size)
+              void *closure)
 {
   jmp_buf jb;
   Word *stackHot = (void *)&jb;
@@ -38,7 +38,7 @@ Res StackScan(ScanState ss, Word *stackCold,
   (void)setjmp(jb);
 
   return StackScanInner(ss, stackCold, stackHot, sizeof jb / sizeof(Word),
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
 }
 
 
diff --git a/mps/code/ssixi3.c b/mps/code/ssixi3.c
index 56fb1290a66..a922cabc5a6 100644
--- a/mps/code/ssixi3.c
+++ b/mps/code/ssixi3.c
@@ -51,7 +51,7 @@ SRCID(ssixi3, "$Id$");
 
 Res StackScan(ScanState ss, Word *stackCold,
               mps_area_scan_t scan_area,
-              void *closure, size_t closure_size)
+              void *closure)
 {
   Word calleeSaveRegs[4];
 
@@ -65,7 +65,7 @@ Res StackScan(ScanState ss, Word *stackCold,
   ASMV("mov %%ebp, %0" : "=m" (calleeSaveRegs[3]));
   
   return StackScanInner(ss, stackCold, calleeSaveRegs, NELEMS(calleeSaveRegs),
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
 }
 
 
diff --git a/mps/code/ssixi6.c b/mps/code/ssixi6.c
index 71a3dd40cf2..2d70d62697c 100644
--- a/mps/code/ssixi6.c
+++ b/mps/code/ssixi6.c
@@ -49,7 +49,7 @@ SRCID(ssixi6, "$Id$");
 
 Res StackScan(ScanState ss, Word *stackCold,
               mps_area_scan_t scan_area,
-              void *closure, size_t closure_size)
+              void *closure)
 {
   Word calleeSaveRegs[6];
   
@@ -65,7 +65,7 @@ Res StackScan(ScanState ss, Word *stackCold,
   ASMV("mov %%r15, %0" : "=m" (calleeSaveRegs[5]));
   
   return StackScanInner(ss, stackCold, calleeSaveRegs, NELEMS(calleeSaveRegs),
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
 }
 
 
diff --git a/mps/code/ssw3i3mv.c b/mps/code/ssw3i3mv.c
index da95ebb106d..2b2d0bd4d08 100644
--- a/mps/code/ssw3i3mv.c
+++ b/mps/code/ssw3i3mv.c
@@ -24,7 +24,7 @@ SRCID(ssw3i3mv, "$Id$");
 
 Res StackScan(ScanState ss, Word *stackCold,
               mps_area_scan_t scan_area,
-              void *closure, size_t closure_size)
+              void *closure)
 {
   jmp_buf jb;
 
@@ -45,7 +45,7 @@ Res StackScan(ScanState ss, Word *stackCold,
   AVER(offsetof(_JUMP_BUFFER, Esi) == offsetof(_JUMP_BUFFER, Ebx) + 8);
 
   return StackScanInner(ss, stackCold, (Word *)&((_JUMP_BUFFER *)jb)->Ebx, 3,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
 }
 
 /* C. COPYRIGHT AND LICENSE
diff --git a/mps/code/ssw3i3pc.c b/mps/code/ssw3i3pc.c
index 913a3d5a035..bead20fe898 100644
--- a/mps/code/ssw3i3pc.c
+++ b/mps/code/ssw3i3pc.c
@@ -48,7 +48,7 @@ typedef struct __JUMP_BUFFER {
 
 Res StackScan(ScanState ss, Word *stackCold,
               mps_area_scan_t scan_area,
-              void *closure, size_t closure_size)
+              void *closure)
 {
   jmp_buf jb;
 
@@ -68,7 +68,7 @@ Res StackScan(ScanState ss, Word *stackCold,
   AVER(offsetof(_JUMP_BUFFER, Esi) == offsetof(_JUMP_BUFFER, Ebx) + 8);
 
   return StackScanInner(ss, stackCold, (Word *)&((_JUMP_BUFFER *)jb)->Ebx, 3,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
 }
 
 
diff --git a/mps/code/ssw3i6mv.c b/mps/code/ssw3i6mv.c
index 9bc3a8e573b..884424d259c 100644
--- a/mps/code/ssw3i6mv.c
+++ b/mps/code/ssw3i6mv.c
@@ -31,8 +31,8 @@ SRCID(ssw3i6mv, "$Id$");
 
 
 Res StackScan(ScanState ss, Word *stackCold,
-              mps_area_scan_t scan_area,
-              void *closure, size_t closure_size)
+              mps_area_scan_t scan_area
+              void *closure)
 {
   jmp_buf jb;
 
@@ -64,7 +64,7 @@ Res StackScan(ScanState ss, Word *stackCold,
   AVER(offsetof(_JUMP_BUFFER, R15) == offsetof(_JUMP_BUFFER, Rbx) + 64);
 
   return StackScanInner(ss, stackCold, (Word *)&((_JUMP_BUFFER *)jb)->Rbx, 9,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
 }
 
 /* C. COPYRIGHT AND LICENSE
diff --git a/mps/code/th.h b/mps/code/th.h
index 39f1d91133b..29a4d243d1d 100644
--- a/mps/code/th.h
+++ b/mps/code/th.h
@@ -70,7 +70,7 @@ extern Arena ThreadArena(Thread thread);
 
 extern Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
                       mps_area_scan_t scan_area,
-                      void *closure, size_t closure_size);
+                      void *closure);
 
 
 #endif /* th_h */
diff --git a/mps/code/than.c b/mps/code/than.c
index cf41e02f50b..3e2dbaa81a0 100644
--- a/mps/code/than.c
+++ b/mps/code/than.c
@@ -119,10 +119,10 @@ Arena ThreadArena(Thread thread)
 
 Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
                mps_area_scan_t scan_area,
-               void *closure, size_t closure_size)
+               void *closure)
 {
   UNUSED(thread);
-  return StackScan(ss, stackCold, scan_area, closure, closure_size);
+  return StackScan(ss, stackCold, scan_area, closure);
 }
 
 
diff --git a/mps/code/thix.c b/mps/code/thix.c
index 6e51d2a5d5f..219ae33bcdd 100644
--- a/mps/code/thix.c
+++ b/mps/code/thix.c
@@ -241,7 +241,7 @@ Arena ThreadArena(Thread thread)
 
 Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
                mps_area_scan_t scan_area,
-               void *closure, size_t closure_size)
+               void *closure)
 {
   pthread_t self;
   Res res;
@@ -251,7 +251,7 @@ Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
   if(pthread_equal(self, thread->id)) {
     /* scan this thread's stack */
     AVER(thread->alive);
-    res = StackScan(ss, stackCold, scan_area, closure, closure_size);
+    res = StackScan(ss, stackCold, scan_area, closure);
     if(res != ResOK)
       return res;
   } else if (thread->alive) {
@@ -273,12 +273,12 @@ Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
      * stackCold (.stack.full-descend)
      */
     res = TraceScanArea(ss, stackBase, stackLimit,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if(res != ResOK)
       return res;
 
     /* scan the registers in the mutator fault context */
-    res = MutatorFaultContextScan(ss, mfc, scan_area, closure, closure_size);
+    res = MutatorFaultContextScan(ss, mfc, scan_area, closure);
     if(res != ResOK)
       return res;
   }
diff --git a/mps/code/thw3i3.c b/mps/code/thw3i3.c
index e5fa73a8082..03675ed46b2 100644
--- a/mps/code/thw3i3.c
+++ b/mps/code/thw3i3.c
@@ -68,8 +68,7 @@ SRCID(thw3i3, "$Id$");
 
 
 Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
-               mps_area_scan_t scan_area,
-               void *closure, size_t closure_size)
+               mps_area_scan_t scan_area, void *closure)
 {
   DWORD id;
   Res res;
@@ -107,7 +106,7 @@ Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
      * stackCold (.stack.full-descend)
      */
     res = TraceScanArea(ss, stackBase, stackLimit,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if(res != ResOK)
       return res;
 
@@ -118,12 +117,12 @@ Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
      */
     res = TraceScanArea(ss, (Word *)&context,
                         (Word *)((char *)&context + sizeof(CONTEXT)),
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if(res != ResOK)
       return res;
 
   } else { /* scan this thread's stack */
-    res = StackScan(ss, stackCold, scan_area, closure, closure_size);
+    res = StackScan(ss, stackCold, scan_area, closure);
     if(res != ResOK)
       return res;
   }
diff --git a/mps/code/thw3i6.c b/mps/code/thw3i6.c
index 090c2c43aa9..67350022ad6 100644
--- a/mps/code/thw3i6.c
+++ b/mps/code/thw3i6.c
@@ -69,7 +69,7 @@ SRCID(thw3i6, "$Id$");
 
 Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
                mps_area_scan_t scan_area,
-               void *closure, size_t closure_size)
+               void *closure)
 {
   DWORD id;
   Res res;
@@ -107,7 +107,7 @@ Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
      * stackCold (.stack.full-descend)
      */
     res = TraceScanArea(ss, stackBase, stackLimit,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if(res != ResOK)
       return res;
 
@@ -118,12 +118,12 @@ Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
      */
     res = TraceScanArea(ss, (Word *)&context,
                         (Word *)((char *)&context + sizeof(CONTEXT)),
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if(res != ResOK)
       return res;
 
   } else { /* scan this thread's stack */
-    res = StackScan(ss, stackCold, scan_area, closure, closure_size);
+    res = StackScan(ss, stackCold, scan_area, closure);
     if(res != ResOK)
       return res;
   }
diff --git a/mps/code/thxc.c b/mps/code/thxc.c
index e5277072dc5..3bb449d46fe 100644
--- a/mps/code/thxc.c
+++ b/mps/code/thxc.c
@@ -211,8 +211,7 @@ Arena ThreadArena(Thread thread)
 #include "prmcxc.h"
 
 Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
-               mps_area_scan_t scan_area,
-               void *closure, size_t closure_size)
+               mps_area_scan_t scan_area, void *closure)
 {
   mach_port_t self;
   Res res;
@@ -223,7 +222,7 @@ Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
   if (thread->port == self) {
     /* scan this thread's stack */
     AVER(thread->alive);
-    res = StackScan(ss, stackCold, scan_area, closure, closure_size);
+    res = StackScan(ss, stackCold, scan_area, closure);
     if(res != ResOK)
       return res;
   } else if (thread->alive) {
@@ -261,12 +260,12 @@ Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
      * stackCold (.stack.full-descend)
      */
     res = TraceScanArea(ss, stackBase, stackLimit,
-                        scan_area, closure, closure_size);
+                        scan_area, closure);
     if(res != ResOK)
       return res;
 
     /* scan the registers in the mutator fault context */
-    res = MutatorFaultContextScan(ss, &mfcStruct, scan_area, closure, closure_size);
+    res = MutatorFaultContextScan(ss, &mfcStruct, scan_area, closure);
     if(res != ResOK)
       return res;
   }
diff --git a/mps/code/trace.c b/mps/code/trace.c
index 001c5b90526..10592f7df2e 100644
--- a/mps/code/trace.c
+++ b/mps/code/trace.c
@@ -1432,7 +1432,7 @@ void TraceScanSingleRef(TraceSet ts, Rank rank, Arena arena,
 
 Res TraceScanArea(ScanState ss, Word *base, Word *limit,
                   mps_area_scan_t scan_area,
-                  void *closure, size_t closure_size)
+                  void *closure)
 {
   AVERT(ScanState, ss);
   AVER(base != NULL);
@@ -1446,7 +1446,7 @@ Res TraceScanArea(ScanState ss, Word *base, Word *limit,
      scan_area. */
   ss->scannedSize += AddrOffset(base, limit);
   
-  return scan_area(&ss->ss_s, base, limit, closure, closure_size);
+  return scan_area(&ss->ss_s, base, limit, closure);
 }
 
 
diff --git a/mps/manual/source/topic/root.rst b/mps/manual/source/topic/root.rst
index 743c865f6a5..3b49d120a3f 100644
--- a/mps/manual/source/topic/root.rst
+++ b/mps/manual/source/topic/root.rst
@@ -489,7 +489,7 @@ Root interface
         requires expertise with the platform's virtual memory
         interface.
 
-.. c:function:: mps_res_t mps_root_create_thread_scanned(mps_root_t *root_o, mps_arena_t arena, mps_rank_t rank, mps_rm_t rm, mps_thr_t thread, mps_area_scan_t scan_area, void *closure, size_t closure_size, void *cold)
+.. c:function:: mps_res_t mps_root_create_thread_scanned(mps_root_t *root_o, mps_arena_t arena, mps_rank_t rank, mps_rm_t rm, mps_thr_t thread, mps_area_scan_t scan_area, void *closure, void *cold)
 
     Register a :term:`root` that consists of the :term:`references` in
     a :term:`thread's <thread>` registers and stack, scanned by an
@@ -511,13 +511,9 @@ Root interface
     :c:func:`mps_scan_area`, or a similar user-defined function. See
     :ref:`topic-scanning-area`.
 
-    ``closure`` is an arbitrary pointer that is passed to ``scan_area``
+    ``closure`` is an arbitrary pointer that will be passed to ``scan_area``
     and intended to point to any parameters it needs.
 
-    ``closure_size`` is an arbitrary size that is passed to
-    ``scan_area`` but is conventionally the size of the parameter
-    object pointer to by ``closure``.
-
     ``cold`` is a pointer to the :term:`cold end` of stack to be
     scanned. On platforms where the stack grows downwards (currently,
     all supported platforms), locations below this address will be
@@ -531,7 +527,7 @@ Root interface
     The registered root description persists until it is destroyed by
     calling :c:func:`mps_root_destroy`.
 
-.. c:function:: mps_res_t mps_root_create_area(mps_root_t *root_o, mps_arena_t arena, mps_rank_t rank, mps_rm_t rm, void *base, void *limit, mps_area_scan_t scan_area, void *closure, size_t closure_size)
+.. c:function:: mps_res_t mps_root_create_area(mps_root_t *root_o, mps_arena_t arena, mps_rank_t rank, mps_rm_t rm, void *base, void *limit, mps_area_scan_t scan_area, void *closure)
 
     Register a :term:`root` that consists of an area of memory scanned
     by an area scanning function.
@@ -553,12 +549,8 @@ Root interface
     :c:func:`mps_scan_area`, or a similar user-defined function. See
     :ref:`topic-scanning-area`.
 
-    ``closure`` is an arbitrary pointer that is passed to ``scan_area``
-    and intended to point to any parameters it needs.
-
-    ``closure_size`` is an arbitrary size that is passed to
-    ``scan_area`` but is conventionally the size of the parameter
-    object pointer to by ``closure``.
+    ``closure`` is an arbitrary pointer that will be passed to
+    ``scan_area`` and intended to point to any parameters it needs.
 
     Returns :c:macro:`MPS_RES_OK` if the root was registered
     successfully, :c:macro:`MPS_RES_MEMORY` if the new root
diff --git a/mps/manual/source/topic/scanning.rst b/mps/manual/source/topic/scanning.rst
index cac8d7457e3..eab99c79b2f 100644
--- a/mps/manual/source/topic/scanning.rst
+++ b/mps/manual/source/topic/scanning.rst
@@ -531,7 +531,7 @@ the scanners, found in ``scan.c`` in the MPS source code.
     
         mps_res_t scan(mps_ss_t ss,
                        void *base, void *limit,
-                       void *closure, size_t closure_size);
+                       void *closure);
     
     ``ss`` is the :term:`scan state`.
     
@@ -545,17 +545,11 @@ the scanners, found in ``scan.c`` in the MPS source code.
     :c:func:`mps_root_create_thread_tagged` then it is the value of
     the ``closure`` argument originally passed to that function.
 
-    ``closure_size`` is an arbitrary size, conventionally used for the
-    size of the :term:`closure` pointed to by ``closure``.  For example,
-    if the scanner was originally registered with
-    :c:func:`mps_root_create_thread_tagged` then it is the value of
-    the ``closure_size`` argument originally passed to that function.
-
-.. c:function:: mps_res_t mps_scan_area(mps_ss_t ss, void *base, void *limit, void *closure, size_t closure_size)
+.. c:function:: mps_res_t mps_scan_area(mps_ss_t ss, void *base, void *limit, void *closure)
 
     Scan an area of memory :term:`fixing <fix>` every word.
-    ``closure`` and ``closure_size`` are ignored.  Expects ``base``
-    and ``limit`` to be word-aligned.
+    ``closure`` is ignored.  Expects ``base`` and ``limit`` to be
+    word-aligned.
     
     This scanner is appropriate for use when all words in the area are
     simple untagged references.
@@ -586,7 +580,7 @@ the scanners, found in ``scan.c`` in the MPS source code.
     interpretation depends on which area scanner it is passed to.  See
     the documentation for the individual area scanners.
 
-.. c:function:: mps_res_t mps_scan_area_masked(mps_ss_t ss, void *base, void *limit, void *closure, size_t closure_size)
+.. c:function:: mps_res_t mps_scan_area_masked(mps_ss_t ss, void *base, void *limit, void *closure)
 
     Scan an area of memory :term:`fixing <fix>` every word, but remove
     tag bits before fixing references, and restore them afterwards.
@@ -603,7 +597,7 @@ the scanners, found in ``scan.c`` in the MPS source code.
     references no matter what tag they have.  This can be especially
     useful if you are debugging your tagging scheme.
 
-.. c:function:: mps_res_t mps_scan_area_tagged(mps_ss_t ss, void *base, void *limit, void *closure, size_t closure_size)
+.. c:function:: mps_res_t mps_scan_area_tagged(mps_ss_t ss, void *base, void *limit, void *closure)
 
     Scan an area of memory :term:`fixing <fix>` only words whose
     masked bits match a particular tag pattern.  ``closure`` should
@@ -626,7 +620,7 @@ the scanners, found in ``scan.c`` in the MPS source code.
         version of the pointer.  See
         :c:func:`mps_root_create_thread_tagged`.
 
-.. c:function:: mps_res_t mps_scan_area_tagged_or_zero(mps_ss_t ss, void *base, void *limit, void *closure, size_t closure_size)
+.. c:function:: mps_res_t mps_scan_area_tagged_or_zero(mps_ss_t ss, void *base, void *limit, void *closure)
 
     Scan an area of memory :term:`fixing <fix>` only words whose
     masked bits are zero or match a particular tag pattern.