diff --git a/mps/code/arenavm.c b/mps/code/arenavm.c
index 1b1a15b50bb..81caf8bead5 100644
--- a/mps/code/arenavm.c
+++ b/mps/code/arenavm.c
@@ -1111,7 +1111,7 @@ static Res vmArenaExtend(VMArena vmArena, Size size)
 
   /* .chunk-create.fail: If we fail, try again with a smaller size */
   {
-    int fidelity = 8;  /* max fraction of addr-space we may 'waste' */
+    unsigned fidelity = 8;  /* max fraction of addr-space we may 'waste' */
     Size chunkHalf;
     Size chunkMin = 4 * 1024;  /* typical single page */
     Size sliceSize;
diff --git a/mps/code/bttest.c b/mps/code/bttest.c
index 1b3514c839a..115df4e236d 100644
--- a/mps/code/bttest.c
+++ b/mps/code/bttest.c
@@ -289,7 +289,7 @@ static void obeyCommand(char *command)
           printf("negative integer arguments are invalid\n");
           return;
         }
-        args[argCount] = l;
+        args[argCount] = (unsigned long)l;
         if (newP == p) { /* strtoul failed */
           printf("couldn't parse an integer argument\n");
           return;
diff --git a/mps/code/cbstest.c b/mps/code/cbstest.c
index 0777a08732b..c04c21eba81 100644
--- a/mps/code/cbstest.c
+++ b/mps/code/cbstest.c
@@ -563,7 +563,7 @@ static void find(CBS cbs, void *block, BT alloc, Size size, Bool high,
 
 extern int main(int argc, char *argv[])
 {
-  int i;
+  unsigned i;
   Addr base, limit;
   mps_arena_t mpsArena;
   Arena arena; /* the ANSI arena which we use to allocate the BT */
diff --git a/mps/code/finalcv.c b/mps/code/finalcv.c
index 81f121eeca6..355c841e1ae 100644
--- a/mps/code/finalcv.c
+++ b/mps/code/finalcv.c
@@ -97,7 +97,7 @@ enum {
 
 static void *test(void *arg, size_t s)
 {
-  int i;                        /* index */
+  unsigned i;                        /* index */
   mps_ap_t ap;
   mps_fmt_t fmt;
   mps_chain_t chain;
diff --git a/mps/code/fmtdy.c b/mps/code/fmtdy.c
index b7a2f7fa02f..21d47080d8e 100644
--- a/mps/code/fmtdy.c
+++ b/mps/code/fmtdy.c
@@ -692,10 +692,14 @@ static mps_addr_t dylan_skip(mps_addr_t object)
 
 static void dylan_copy(mps_addr_t old, mps_addr_t new)
 {
-  size_t length = (char *)dylan_skip(old) - (char *)old;
+  char *base = (char *)old;
+  char *limit = (char *)dylan_skip(old);
+  size_t length;
+  assert(base < limit);
+  length = (size_t)(limit - base);
   assert(dylan_wrapper_check(*(mps_word_t **)old));
   /* .improve.memcpy: Can do better here as we know that new and old
-   * will be aligned (to MPS_PF_ALIGN) */
+     will be aligned (to MPS_PF_ALIGN) */
   (void)memcpy(new, old, length);
 }
 
diff --git a/mps/code/mps.xcodeproj/project.pbxproj b/mps/code/mps.xcodeproj/project.pbxproj
index 8f71736f689..cbee78a359f 100644
--- a/mps/code/mps.xcodeproj/project.pbxproj
+++ b/mps/code/mps.xcodeproj/project.pbxproj
@@ -3213,7 +3213,6 @@
 				GCC_VERSION = com.apple.compilers.llvm.clang.1_0;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_INVALID_OFFSETOF_MACRO = NO;
-				GCC_WARN_ABOUT_MISSING_FIELD_INITIALIZERS = YES;
 				GCC_WARN_ABOUT_MISSING_NEWLINE = YES;
 				GCC_WARN_ABOUT_MISSING_PROTOTYPES = YES;
 				GCC_WARN_ABOUT_RETURN_TYPE = YES;
@@ -3270,7 +3269,6 @@
 				GCC_VERSION = com.apple.compilers.llvm.clang.1_0;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_INVALID_OFFSETOF_MACRO = NO;
-				GCC_WARN_ABOUT_MISSING_FIELD_INITIALIZERS = YES;
 				GCC_WARN_ABOUT_MISSING_NEWLINE = YES;
 				GCC_WARN_ABOUT_MISSING_PROTOTYPES = YES;
 				GCC_WARN_ABOUT_RETURN_TYPE = YES;
diff --git a/mps/code/mv2test.c b/mps/code/mv2test.c
index b2f7fcf7ea8..2937aafc807 100644
--- a/mps/code/mv2test.c
+++ b/mps/code/mv2test.c
@@ -76,7 +76,7 @@ static float ran1(long *idum)
   *idum=IA*(*idum-k*IQ)-IR*k;   /* Compute idum=(IA*idum) % IM without
                                    overflows by Schrage's method. */
   if (*idum < 0) *idum += IM;
-  j=iy/NDIV;                    /* Will be in the range 0..NTAB-1. */
+  j=(int)(iy/NDIV);             /* Will be in the range 0..NTAB-1. */
   iy=iv[j];                     /* Output previously stored value and
                                    refill the shuffle table. */
   iv[j] = *idum;
diff --git a/mps/code/poolmrg.c b/mps/code/poolmrg.c
index a8c08047821..73ec8ac81f1 100644
--- a/mps/code/poolmrg.c
+++ b/mps/code/poolmrg.c
@@ -347,7 +347,7 @@ static RefPart MRGRefPartOfLink(Link link, Arena arena)
   AVERT(MRGLinkSeg, linkseg);
   linkBase = (Link)SegBase(seg);
   AVER(link >= linkBase);
-  index = link - linkBase;
+  index = (Index)(link - linkBase);
   AVER(index < MRGGuardiansPerSeg(Pool2MRG(SegPool(seg))));
 
   return refPartOfIndex(linkseg->refSeg, index);
@@ -475,7 +475,7 @@ static MessageClassStruct MRGMessageClassStruct = {
  * .segpair.destroy: We don't worry about the effect that destroying
  * these segs has on any of the pool rings.
  */
-static void MRGSegPairDestroy(MRGRefSeg refseg, MRG mrg)
+static void MRGSegPairDestroy(MRGRefSeg refseg)
 {
   RingRemove(&refseg->mrgRing);
   RingFinish(&refseg->mrgRing);
@@ -678,7 +678,7 @@ static void MRGFinish(Pool pool)
 
   RING_FOR(node, &mrg->refRing, nextNode) {
     MRGRefSeg refseg = RING_ELT(MRGRefSeg, mrgRing, node);
-    MRGSegPairDestroy(refseg, mrg);
+    MRGSegPairDestroy(refseg);
   }
 
   mrg->sig = SigInvalid;
diff --git a/mps/code/protsgix.c b/mps/code/protsgix.c
index ee47676a933..80a2f94dff0 100644
--- a/mps/code/protsgix.c
+++ b/mps/code/protsgix.c
@@ -79,18 +79,18 @@ static void sigHandle(int sig, siginfo_t *info, void *context)  /* .sigh.args */
   sigset_t asigset, oldset;
   struct sigaction sa;
 
+  UNUSED(context);
   AVER(sig == PROT_SIGNAL);
 
   /* .sigh.context */
   if(PROT_SIGINFO_GOOD(info)) {
     AccessSet mode;
-    Addr base, limit;
+    Addr base;
 
     mode = AccessREAD | AccessWRITE; /* .sigh.mode */
 
     /* We assume that the access is for one word at the address. */
     base = (Addr)info->si_addr;   /* .sigh.context */
-    limit = AddrAdd(base, (Size)sizeof(Addr));
 
     /* Offer each protection structure the opportunity to handle the */
     /* exception.  If it succeeds, then allow the mutator to continue. */
diff --git a/mps/code/steptest.c b/mps/code/steptest.c
index ad1e2359508..7236e9aaa9c 100644
--- a/mps/code/steptest.c
+++ b/mps/code/steptest.c
@@ -59,7 +59,7 @@ static unsigned long step_frequencies[] = {
 
 #define TESTS (sizeof(step_frequencies) / sizeof(step_frequencies[0]))
 
-static int test_number = 0;
+static unsigned test_number = 0;
 
 
 /* objNULL needs to be odd so that it's ignored in exactRoots. */
diff --git a/mps/code/testlib.c b/mps/code/testlib.c
index 027cbd2f9cd..d7f4bc60418 100644
--- a/mps/code/testlib.c
+++ b/mps/code/testlib.c
@@ -258,7 +258,7 @@ void randomize(int argc, char **argv)
   } else {
     /* time_t uses an arbitrary encoding, but hopefully the low order */
     /* 31 bits will have at least one bit changed from run to run. */
-    seedt = 1 + time(NULL) % (R_m - 1);
+    seedt = 1 + (unsigned long)time(NULL) % (R_m - 1);
 
     /* The value returned by time() on some OSs may simply be a 
      * count of seconds: therefore successive runs may start with 
diff --git a/mps/code/trace.c b/mps/code/trace.c
index 82b3047f1c7..a12800d4dd9 100644
--- a/mps/code/trace.c
+++ b/mps/code/trace.c
@@ -1667,7 +1667,7 @@ void TraceStart(Trace trace, double mortality, double finishingTime)
     if(nPolls >= (double)LONG_MAX)
       nPolls = (double)LONG_MAX;
     /* rate equals scanning work per number of polls available */
-    trace->rate = (trace->foundation + sSurvivors) / (long)nPolls + 1;
+    trace->rate = (trace->foundation + sSurvivors) / (unsigned long)nPolls + 1;
   }
 
   /* @@ DIAG for rate of scanning here. */
diff --git a/mps/code/vmix.c b/mps/code/vmix.c
index f5ba622f7c9..0718dd982fa 100644
--- a/mps/code/vmix.c
+++ b/mps/code/vmix.c
@@ -116,8 +116,7 @@ Res VMCreate(VM *vmReturn, Size size)
   /* type Align. */
   AVER(pagesize > 0);
   AVER((unsigned long)pagesize <= (unsigned long)(Align)-1);
-  /* Note implicit conversion from "int" to "Align". */
-  align = pagesize;
+  align = (Align)pagesize;
   AVER(SizeIsP2(align));
   size = SizeAlignUp(size, align);
   if((size == 0) || (size > (Size)(size_t)-1))
diff --git a/mps/code/zcoll.c b/mps/code/zcoll.c
index 70f77b2b4c7..494b443e6b7 100644
--- a/mps/code/zcoll.c
+++ b/mps/code/zcoll.c
@@ -681,7 +681,7 @@ static void testscriptC(mps_arena_t arena, mps_ap_t ap, const char *script)
         checksi(si, 1, script, scriptAll);
         script += sb;
         printf("  StackScan(%u)\n", on);
-        StackScan(arena, on);
+        StackScan(arena, on != 0);
         break;
       }
       case 'Z': {