diff --git a/src/c/cmpaux.d b/src/c/cmpaux.d
index 1033620d9..c2d36f15f 100644
--- a/src/c/cmpaux.d
+++ b/src/c/cmpaux.d
@@ -166,7 +166,7 @@ aset_bv(cl_object x, cl_index index, int value)
 void
 cl_throw(cl_object tag)
 {
-  ecl_frame_ptr fr = frs_sch_catch(tag);
+  ecl_frame_ptr fr = frs_sch(tag);
   if (fr == NULL)
     FEcontrol_error("THROW: The catch ~S is undefined.", 1, tag);
   unwind(fr);
diff --git a/src/c/eval.d b/src/c/eval.d
index 260e7ef5a..730bca7d8 100644
--- a/src/c/eval.d
+++ b/src/c/eval.d
@@ -252,14 +252,13 @@ cl_safe_eval(cl_object form, cl_object env, cl_object err_value)
 {
 	cl_object output;
 
-	if (frs_push(FRS_CATCHALL, Cnil)) {
-		output = err_value;
-	} else {
+	CL_CATCH_ALL_BEGIN
 		bds_bind(@'si::*ignore-errors*', Ct);
 		output = si_eval_with_env(2, form, env);
 		bds_unwind1();
-	}
-	frs_pop();
+	CL_CATCH_ALL_IF_CAUGHT
+		output = err_value;
+	CL_CATCH_ALL_END;
 	return output;
 }
 
diff --git a/src/c/interpreter.d b/src/c/interpreter.d
index aa92ba10f..89052edeb 100644
--- a/src/c/interpreter.d
+++ b/src/c/interpreter.d
@@ -1096,7 +1096,7 @@ interpret(cl_object bytecodes, void *pc) {
 		name = GET_DATA(vector, bytecodes);
 		GET_LABEL(exit, vector);
 		cl_stack_push((cl_object)exit);
-		if (frs_push(FRS_CATCH, id) == 0) {
+		if (frs_push(id) == 0) {
 			bind_block(name, id);
 		} else {
 			reg0 = VALUES(0);
@@ -1120,7 +1120,7 @@ interpret(cl_object bytecodes, void *pc) {
 		/* FIXME! */
 		GET_LABEL(exit, vector);
 		cl_stack_push((cl_object)exit);
-		if (frs_push(FRS_CATCH, id) == 0) {
+		if (frs_push(id) == 0) {
 			bind_block(name, id);
 		} else {
 			reg0 = VALUES(0);
@@ -1142,7 +1142,7 @@ interpret(cl_object bytecodes, void *pc) {
 		cl_opcode *exit;
 		GET_LABEL(exit, vector);
 		cl_stack_push((cl_object)exit);
-		if (frs_push(FRS_CATCH, reg0) != 0) {
+		if (frs_push(reg0) != 0) {
 			reg0 = VALUES(0);
 			cl_env.lex_env = cl_env.frs_top->frs_lex;
 			frs_pop();
@@ -1166,7 +1166,7 @@ interpret(cl_object bytecodes, void *pc) {
 		int n = GET_OPARG(vector);
 		/* Here we save the location of the jump table */
 		cl_stack_push((cl_object)vector); /* FIXME! */
-		if (frs_push(FRS_CATCH, bind_tagbody()) == 0) {
+		if (frs_push(bind_tagbody()) == 0) {
 			/* The first time, we "name" the tagbody and
 			 * skip the jump table */
 			vector += n * OPARG_SIZE;
@@ -1309,7 +1309,7 @@ interpret(cl_object bytecodes, void *pc) {
 		cl_opcode *exit;
 		GET_LABEL(exit, vector);
 		cl_stack_push((cl_object)exit);
-		if (frs_push(FRS_PROTECT,Cnil) != 0) {
+		if (frs_push(ECL_PROTECT_TAG) != 0) {
 			cl_env.lex_env = cl_env.frs_top->frs_lex;
 			frs_pop();
 			vector = (cl_opcode *)cl_stack_pop();
diff --git a/src/c/main.d b/src/c/main.d
index 5d8154200..e9e0442b3 100644
--- a/src/c/main.d
+++ b/src/c/main.d
@@ -128,12 +128,11 @@ cl_shutdown(void)
 {
 	cl_object l = SYM_VAL(@'si::*exit-hooks*');
 	while (CONSP(l)) {
-		if (!frs_push(FRS_CATCHALL, Cnil)) {
+		CL_CATCH_ALL_BEGIN
 			bds_bind(@'si::*ignore-errors*', Ct);
 			funcall(1, CAR(l));
 			bds_unwind1();
-		}
-		frs_pop();
+		CL_CATCH_ALL_END;
 		l = CDR(l);
 	}
 #ifdef ENABLE_DLOPEN
diff --git a/src/c/stacks.d b/src/c/stacks.d
index e6ba2293d..c541f2842 100644
--- a/src/c/stacks.d
+++ b/src/c/stacks.d
@@ -255,13 +255,12 @@ frs_overflow(void)		/* used as condition in list.d */
 }
 
 ecl_frame_ptr
-_frs_push(register enum fr_class clas, register cl_object val)
+_frs_push(register cl_object val)
 {
 	ecl_frame_ptr output = ++cl_env.frs_top;
 	if (output >= cl_env.frs_limit) frs_overflow();
 	output->frs_lex = cl_env.lex_env;
 	output->frs_bds_top = cl_env.bds_top;
-	output->frs_class = clas;
 	output->frs_val = val;
 	output->frs_ihs = cl_env.ihs_top;
 	output->frs_sp = cl_stack_index();
@@ -272,7 +271,7 @@ void
 unwind(ecl_frame_ptr fr)
 {
 	cl_env.nlj_fr = fr;
-	while (cl_env.frs_top != fr && cl_env.frs_top->frs_class == FRS_CATCH)
+	while (cl_env.frs_top != fr && cl_env.frs_top->frs_val != ECL_PROTECT_TAG)
 		--cl_env.frs_top;
 	cl_env.lex_env = cl_env.frs_top->frs_lex;
 	cl_env.ihs_top = cl_env.frs_top->frs_ihs;
@@ -288,23 +287,11 @@ frs_sch (cl_object frame_id)
 	ecl_frame_ptr top;
 
 	for (top = cl_env.frs_top;  top >= cl_env.frs_org;  top--)
-		if (top->frs_val == frame_id && top->frs_class == FRS_CATCH)
+		if (top->frs_val == frame_id)
 			return(top);
 	return(NULL);
 }
 
-ecl_frame_ptr
-frs_sch_catch(cl_object frame_id)
-{
-	ecl_frame_ptr top;
-
-	for(top = cl_env.frs_top;  top >= cl_env.frs_org  ;top--)
-	  if ((top->frs_val == frame_id && top->frs_class == FRS_CATCH)
-	      || top->frs_class == FRS_CATCHALL)
-	    return(top);
-	return(NULL);
-}
-
 static ecl_frame_ptr
 get_frame_ptr(cl_object x)
 {
@@ -330,20 +317,6 @@ si_frs_bds(cl_object arg)
 	@(return MAKE_FIXNUM(get_frame_ptr(arg)->frs_bds_top - cl_env.bds_org))
 }
 
-cl_object
-si_frs_class(cl_object arg)
-{
-	enum fr_class c;
-	cl_object output;
-
-	c = get_frame_ptr(arg)->frs_class;
-	if (c == FRS_CATCH) output = @':catch';
-	else if (c == FRS_PROTECT) output = @':protect';
-	else if (c == FRS_CATCHALL) output = @':catchall';
-	else FEerror("Unknown frs class was detected.", 0);
-	@(return output)
-}
-
 cl_object
 si_frs_tag(cl_object arg)
 {
diff --git a/src/c/symbols_list.h b/src/c/symbols_list.h
index 154459c26..1af45c7c5 100644
--- a/src/c/symbols_list.h
+++ b/src/c/symbols_list.h
@@ -1098,7 +1098,6 @@ cl_symbols[] = {
 {SYS_ "FORMATTER-AUX", SI_ORDINARY, si_formatter_aux, -1, OBJNULL},
 #endif
 {SYS_ "FRS-BDS", SI_ORDINARY, si_frs_bds, 1, OBJNULL},
-{SYS_ "FRS-CLASS", SI_ORDINARY, si_frs_class, 1, OBJNULL},
 {SYS_ "FRS-IHS", SI_ORDINARY, si_frs_ihs, 1, OBJNULL},
 {SYS_ "FRS-TAG", SI_ORDINARY, si_frs_tag, 1, OBJNULL},
 {SYS_ "FRS-TOP", SI_ORDINARY, si_frs_top, 0, OBJNULL},
@@ -1300,8 +1299,6 @@ cl_symbols[] = {
 {KEY_ "BLOCK", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "CAPITALIZE", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "CASE", KEYWORD, NULL, -1, OBJNULL},
-{KEY_ "CATCH", KEYWORD, NULL, -1, OBJNULL},
-{KEY_ "CATCHALL", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "CIRCLE", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "COMPILE-TOPLEVEL", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "COMMON",KEYWORD,NULL,-1,OBJNULL},
@@ -1387,7 +1384,6 @@ cl_symbols[] = {
 {KEY_ "PRINT-FUNCTION", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "PRINT-OBJECT", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "PROBE", KEYWORD, NULL, -1, OBJNULL},
-{KEY_ "PROTECT", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "RADIX", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "READABLY", KEYWORD, NULL, -1, OBJNULL},
 {KEY_ "REHASH-SIZE", KEYWORD, NULL, -1, OBJNULL},
diff --git a/src/c/symbols_list2.h b/src/c/symbols_list2.h
index 6783e18f2..f80cafb60 100644
--- a/src/c/symbols_list2.h
+++ b/src/c/symbols_list2.h
@@ -1098,7 +1098,6 @@ cl_symbols[] = {
 {SYS_ "FORMATTER-AUX","si_formatter_aux"},
 #endif
 {SYS_ "FRS-BDS","si_frs_bds"},
-{SYS_ "FRS-CLASS","si_frs_class"},
 {SYS_ "FRS-IHS","si_frs_ihs"},
 {SYS_ "FRS-TAG","si_frs_tag"},
 {SYS_ "FRS-TOP","si_frs_top"},
@@ -1300,8 +1299,6 @@ cl_symbols[] = {
 {KEY_ "BLOCK",NULL},
 {KEY_ "CAPITALIZE",NULL},
 {KEY_ "CASE",NULL},
-{KEY_ "CATCH",NULL},
-{KEY_ "CATCHALL",NULL},
 {KEY_ "CIRCLE",NULL},
 {KEY_ "COMPILE-TOPLEVEL",NULL},
 {KEY_ "COMMON",NULL},
@@ -1387,7 +1384,6 @@ cl_symbols[] = {
 {KEY_ "PRINT-FUNCTION",NULL},
 {KEY_ "PRINT-OBJECT",NULL},
 {KEY_ "PROBE",NULL},
-{KEY_ "PROTECT",NULL},
 {KEY_ "RADIX",NULL},
 {KEY_ "READABLY",NULL},
 {KEY_ "REHASH-SIZE",NULL},
diff --git a/src/cmp/cmpblock.lsp b/src/cmp/cmpblock.lsp
index 2b4e6a760..98fe2eaaa 100644
--- a/src/cmp/cmpblock.lsp
+++ b/src/cmp/cmpblock.lsp
@@ -62,7 +62,7 @@
 	    (wt-nl "volatile cl_object env" (incf *env-lvl*)
 		   " = env" env-lvl ";")))
 	(bind "new_frame_id()" blk-var)
-	(wt-nl "if (frs_push(FRS_CATCH," blk-var ")!=0) {")
+	(wt-nl "if (frs_push(" blk-var ")!=0) {")
 	(let ((*unwind-exit* (cons 'FRAME *unwind-exit*)))
 	  (unwind-exit 'VALUES)
 	  (wt-nl "} else {")
diff --git a/src/cmp/cmpcatch.lsp b/src/cmp/cmpcatch.lsp
index ae09ce1a1..0b99e3f21 100644
--- a/src/cmp/cmpcatch.lsp
+++ b/src/cmp/cmpcatch.lsp
@@ -28,12 +28,12 @@
 	   (*unwind-exit* (list* *exit* 'FRAME *unwind-exit*)))
       (if (member new-destination '(TRASH VALUES))
 	  (progn
-	    (wt-nl "if (frs_push(FRS_CATCH," 'VALUE0 ")==0) {")
+	    (wt-nl "if (frs_push(" 'VALUE0 ")==0) {")
 	    (wt-comment "BEGIN CATCH " code nil)
 	    (c2expr body)
 	    (wt-nl "}"))
 	  (progn
-	    (wt-nl "if (frs_push(FRS_CATCH," 'VALUE0 ")) {")
+	    (wt-nl "if (frs_push(" 'VALUE0 ")) {")
 	    (wt-comment "BEGIN CATCH " code nil)
 	    (unwind-exit 'VALUES t)
 	    (wt-nl "}")
@@ -60,7 +60,7 @@
   (wt-nl "ecl_frame_ptr next_fr; cl_object next_tag;")
   ;; Here we compile the form which is protected. When this form
   ;; is aborted, it continues at the frs_pop() with unwinding=TRUE.
-  (wt-nl "if (frs_push(FRS_PROTECT,Cnil)) {")
+  (wt-nl "if (frs_push(ECL_PROTECT_TAG)) {")
   (wt-nl "unwinding = TRUE; next_fr=cl_env.nlj_fr; } else {")
   (let ((*unwind-exit* (cons 'FRAME *unwind-exit*))
 	(*destination* 'VALUES))
diff --git a/src/cmp/cmptag.lsp b/src/cmp/cmptag.lsp
index a4efef2f0..0155e14dd 100644
--- a/src/cmp/cmptag.lsp
+++ b/src/cmp/cmptag.lsp
@@ -132,7 +132,7 @@
 	  (wt-nl "{ cl_object " tag-loc ";")
 	  (setq env-grows t))		; just to ensure closing the block
 	(bind "new_frame_id()" tag-loc)
-	(wt-nl "if (frs_push(FRS_CATCH," tag-loc ")) {")
+	(wt-nl "if (frs_push(" tag-loc ")) {")
 	;; Allocate labels.
 	(dolist (tag body)
 	  (when (and (tag-p tag) (plusp (tag-ref tag)))
diff --git a/src/cmp/sysfun.lsp b/src/cmp/sysfun.lsp
index 0b402613c..2cb1633c7 100644
--- a/src/cmp/sysfun.lsp
+++ b/src/cmp/sysfun.lsp
@@ -306,7 +306,6 @@
 (proclaim-function si:frs-top (*) t)
 (proclaim-function si::frs-vs (*) t)
 (proclaim-function si:frs-bds (*) t)
-(proclaim-function si:frs-class (*) t)
 (proclaim-function si:frs-tag (*) t)
 (proclaim-function si:frs-ihs (*) t)
 (proclaim-function si:bds-top (*) t)
diff --git a/src/h/external.h b/src/h/external.h
index 7614fc304..ccbdc4933 100644
--- a/src/h/external.h
+++ b/src/h/external.h
@@ -1229,7 +1229,6 @@ extern cl_object si_ihs_next(cl_object arg);
 extern cl_object si_ihs_prev(cl_object arg);
 extern cl_object si_frs_top(void);
 extern cl_object si_frs_bds(cl_object arg);
-extern cl_object si_frs_class(cl_object arg);
 extern cl_object si_frs_tag(cl_object arg);
 extern cl_object si_frs_ihs(cl_object arg);
 extern cl_object si_bds_top(void);
diff --git a/src/h/stacks.h b/src/h/stacks.h
index c9398700a..e784daf4b 100644
--- a/src/h/stacks.h
+++ b/src/h/stacks.h
@@ -92,40 +92,38 @@ extern cl_object ihs_top_function_name(void);
 /***************
  * FRAME STACK
  ***************/
-/*
-frs_class |            frs_value                 |  frs_prev
-----------+--------------------------------------+--------------
-CATCH     | frame-id, i.e.                       |
-	  |    throw-tag,                        |
-	  |    block-id (uninterned symbol), or  | value of ihs_top
-	  |    tagbody-id (uninterned symbol)    | when the frame
-----------+--------------------------------------| was pushed
-CATCHALL  |               NIL                    |
-----------+--------------------------------------|
-PROTECT   |               NIL                    |
-----------------------------------------------------------------
-*/
-
-enum fr_class {
-	FRS_CATCH,		/* for catch,block,tabbody */
-	FRS_CATCHALL,		/* for catchall */
-	FRS_PROTECT		/* for protect-all */
-};
+/* Frames signal points in the code to which we can at any time jump.
+ * Frames are established, for instance, by CATCH, BLOCK, TAGBODY,
+ * LAMBDA, UNWIND-PROTECT, etc.
+ *
+ * Frames are established by frs_push(). For each call to frs_push()
+ * there must be a corresponding frs_pop(). More precisely, since our
+ * frame mechanism relies on the C stack and on the setjmp/longjmp
+ * functions, any function that creates a frame must also destroy it
+ * with frs_pop() before returning.
+ *
+ * Frames are identified by a value frs_val. This can be either a
+ * unique identifier, created for each CATCH, BLOCK, etc, or a common
+ * one ECL_PROTECT_TAG, used by UNWIND-PROTECT forms. The first type
+ * of frames can be target of a search frs_sch() and thus one can jump
+ * to them. The second type of frames are like barriers designed to
+ * intercept the jumps to the outer frames and are called
+ * automatically by the function unwind() whenever it jumps to a frame
+ * which is beyond one of these barriers.
+ */
 
 typedef struct ecl_frame {
 	jmp_buf		frs_jmpbuf;
+	cl_object	frs_val;
 	cl_object	frs_lex;
 	bds_ptr		frs_bds_top;
-	enum fr_class	frs_class;
-	cl_object	frs_val;
 	ihs_ptr		frs_ihs;
 	cl_index	frs_sp;
 } *ecl_frame_ptr;
 
-extern ecl_frame_ptr _frs_push(register enum fr_class clas, register cl_object val);
-
-#define frs_push(class, val)  ecl_setjmp(_frs_push(class, val)->frs_jmpbuf)
-
+#define ECL_PROTECT_TAG OBJNULL
+extern ecl_frame_ptr _frs_push(register cl_object val);
+#define frs_push(val)  ecl_setjmp(_frs_push(val)->frs_jmpbuf)
 #define frs_pop() (cl_env.frs_top--)
 
 /*******************
@@ -178,7 +176,7 @@ cl_env.lex_env ------> ( tag0 value0 tag1 value1 ... )
 #define CL_UNWIND_PROTECT_BEGIN {\
 	bool __unwinding; ecl_frame_ptr __next_fr; \
 	cl_index __nr; \
-	if (frs_push(FRS_PROTECT,Cnil)) { \
+	if (frs_push(ECL_PROTECT_TAG)) { \
 		__unwinding=1; __next_fr=cl_env.nlj_fr; \
 	} else {
 
@@ -193,19 +191,19 @@ cl_env.lex_env ------> ( tag0 value0 tag1 value1 ... )
 
 #define CL_BLOCK_BEGIN(id) { \
 	cl_object id = new_frame_id(); \
-	if (frs_push(FRS_CATCH,id) == 0)
+	if (frs_push(id) == 0)
 
 #define CL_BLOCK_END } \
 	frs_pop()
 
 #define CL_CATCH_BEGIN(tag) \
-	if (frs_push(FRS_CATCH,tag) == 0) {
+	if (frs_push(tag) == 0) {
 
 #define CL_CATCH_END } \
 	frs_pop();
 
 #define CL_CATCH_ALL_BEGIN \
-	if (frs_push(FRS_CATCH,Cnil) == 0) {
+	if (frs_push(ECL_PROTECT_TAG) == 0) {
 
 #define CL_CATCH_ALL_IF_CAUGHT } else {