diff --git a/libguile/control.c b/libguile/control.c
index dc3fed250..9121d1791 100644
--- a/libguile/control.c
+++ b/libguile/control.c
@@ -163,7 +163,7 @@ reify_partial_continuation (SCM vm, SCM prompt, SCM extwinds,
   /* Since non-escape continuations should begin with a thunk application, the
      first bit of the stack should be a frame, with the saved fp equal to the fp
      that was current when the prompt was made. */
-  if ((SCM*)(SCM_PROMPT_REGISTERS (prompt)->sp[1])
+  if ((SCM*)SCM_UNPACK (SCM_PROMPT_REGISTERS (prompt)->sp[1])
       != SCM_PROMPT_REGISTERS (prompt)->fp)
     abort ();
 
diff --git a/libguile/eval.c b/libguile/eval.c
index 009f3790b..0101f019e 100644
--- a/libguile/eval.c
+++ b/libguile/eval.c
@@ -102,7 +102,8 @@
  */
 
 static scm_t_bits scm_tc16_boot_closure;
-#define RETURN_BOOT_CLOSURE(code, env) SCM_RETURN_NEWSMOB2 (scm_tc16_boot_closure, (code), (env))
+#define RETURN_BOOT_CLOSURE(code, env) \
+  SCM_RETURN_NEWSMOB2 (scm_tc16_boot_closure, SCM_UNPACK (code), SCM_UNPACK (env))
 #define BOOT_CLOSURE_P(obj) SCM_TYP16_PREDICATE (scm_tc16_boot_closure, (obj))
 #define BOOT_CLOSURE_CODE(x) SCM_SMOB_OBJECT (x)
 #define BOOT_CLOSURE_ENV(x) SCM_SMOB_OBJECT_2 (x)
diff --git a/libguile/frames.c b/libguile/frames.c
index 62ba23fff..2e83cde9a 100644
--- a/libguile/frames.c
+++ b/libguile/frames.c
@@ -124,7 +124,7 @@ SCM_DEFINE (scm_frame_num_locals, "frame-num-locals", 1, 0, 0,
   p = SCM_FRAME_STACK_ADDRESS (SCM_VM_FRAME_FP (frame));
   while (p <= sp)
     {
-      if (p[0] == (SCM)0)
+      if (SCM_UNPACK (p[0]) == 0)
         /* skip over not-yet-active frame */
         p += 3;
       else
@@ -154,7 +154,7 @@ SCM_DEFINE (scm_frame_local_ref, "frame-local-ref", 2, 0, 0,
   p = SCM_FRAME_STACK_ADDRESS (SCM_VM_FRAME_FP (frame));
   while (p <= sp)
     {
-      if (p[0] == (SCM)0)
+      if (SCM_UNPACK (p[0]) == 0)
         /* skip over not-yet-active frame */
         p += 3;
       else if (n == i)
@@ -186,7 +186,7 @@ SCM_DEFINE (scm_frame_local_set_x, "frame-local-set!", 3, 0, 0,
   p = SCM_FRAME_STACK_ADDRESS (SCM_VM_FRAME_FP (frame));
   while (p <= sp)
     {
-      if (p[0] == (SCM)0)
+      if (SCM_UNPACK (p[0]) == 0)
         /* skip over not-yet-active frame */
         p += 3;
       else if (n == i)
diff --git a/libguile/frames.h b/libguile/frames.h
index 3d8a4b27a..47244c7a3 100644
--- a/libguile/frames.h
+++ b/libguile/frames.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2001, 2009, 2010 Free Software Foundation, Inc.
+/* Copyright (C) 2001, 2009, 2010, 2011 Free Software Foundation, Inc.
  * * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -70,15 +70,15 @@
 #define SCM_FRAME_RETURN_ADDRESS(fp)				\
   (SCM_FRAME_BYTE_CAST (SCM_FRAME_DATA_ADDRESS (fp)[2]))
 #define SCM_FRAME_SET_RETURN_ADDRESS(fp, ra)			\
-  ((SCM_FRAME_DATA_ADDRESS (fp)[2])) = (SCM)(ra);
+  ((SCM_FRAME_DATA_ADDRESS (fp)[2])) = SCM_PACK (ra)
 #define SCM_FRAME_MV_RETURN_ADDRESS(fp)				\
   (SCM_FRAME_BYTE_CAST (SCM_FRAME_DATA_ADDRESS (fp)[1]))
 #define SCM_FRAME_SET_MV_RETURN_ADDRESS(fp, mvra)		\
-  ((SCM_FRAME_DATA_ADDRESS (fp)[1])) = (SCM)(mvra);
+  ((SCM_FRAME_DATA_ADDRESS (fp)[1])) = SCM_PACK (mvra)
 #define SCM_FRAME_DYNAMIC_LINK(fp)				\
   (SCM_FRAME_STACK_CAST (SCM_FRAME_DATA_ADDRESS (fp)[0]))
 #define SCM_FRAME_SET_DYNAMIC_LINK(fp, dl)			\
-  ((SCM_FRAME_DATA_ADDRESS (fp)[0])) = (SCM)(dl);
+  ((SCM_FRAME_DATA_ADDRESS (fp)[0])) = SCM_PACK (dl)
 #define SCM_FRAME_VARIABLE(fp,i)	SCM_FRAME_STACK_ADDRESS (fp)[i]
 #define SCM_FRAME_PROGRAM(fp)		SCM_FRAME_STACK_ADDRESS (fp)[-1]
 
diff --git a/libguile/goops.c b/libguile/goops.c
index 1fca49150..33933965c 100644
--- a/libguile/goops.c
+++ b/libguile/goops.c
@@ -293,7 +293,8 @@ SCM_DEFINE (scm_class_of, "class-of", 1, 0, 0,
 	    return scm_class_fraction;
           }
 	case scm_tc7_program:
-	  if (SCM_PROGRAM_IS_PRIMITIVE_GENERIC (x) && *SCM_SUBR_GENERIC (x))
+	  if (SCM_PROGRAM_IS_PRIMITIVE_GENERIC (x)
+              && SCM_UNPACK (*SCM_SUBR_GENERIC (x)))
 	    return scm_class_primitive_generic;
 	  else
 	    return scm_class_procedure;
@@ -494,8 +495,8 @@ compute_getters_n_setters (SCM slots)
       SCM options = SCM_CDAR (slots);
       if (!scm_is_null (options))
 	{
-	  init = scm_get_keyword (k_init_value, options, 0);
-	  if (init)
+	  init = scm_get_keyword (k_init_value, options, SCM_PACK (0));
+	  if (SCM_UNPACK (init))
             {
               init = scm_primitive_eval (scm_list_3 (scm_sym_lambda,
                                                      SCM_EOL,
@@ -592,7 +593,7 @@ SCM_DEFINE (scm_sys_initialize_object, "%initialize-object", 2, 0, 0,
        get_n_set = SCM_CDR (get_n_set), slots = SCM_CDR (slots))
     {
       SCM slot_name  = SCM_CAR (slots);
-      SCM slot_value = 0;
+      SCM slot_value = SCM_PACK (0);
 
       if (!scm_is_null (SCM_CDR (slot_name)))
 	{
@@ -604,10 +605,10 @@ SCM_DEFINE (scm_sys_initialize_object, "%initialize-object", 2, 0, 0,
 	  tmp 	= scm_i_get_keyword (k_init_keyword,
 				     SCM_CDR (slot_name),
 				     n,
-				     0,
+				     SCM_PACK (0),
 				     FUNC_NAME);
 	  slot_name = SCM_CAR (slot_name);
-	  if (tmp)
+	  if (SCM_UNPACK (tmp))
 	    {
 	      /* an initarg was provided for this slot */
 	      if (!scm_is_keyword (tmp))
@@ -616,12 +617,12 @@ SCM_DEFINE (scm_sys_initialize_object, "%initialize-object", 2, 0, 0,
 	      slot_value = scm_i_get_keyword (tmp,
 					      initargs,
 					      n_initargs,
-					      0,
+					      SCM_PACK (0),
 					      FUNC_NAME);
 	    }
 	}
 
-      if (slot_value)
+      if (SCM_UNPACK (slot_value))
 	/* set slot to provided value */
 	set_slot_value (class, obj, SCM_CAR (get_n_set), slot_value);
       else
@@ -1775,7 +1776,7 @@ SCM_DEFINE (scm_primitive_generic_generic, "primitive-generic-generic", 1, 0, 0,
 {
   if (SCM_PRIMITIVE_GENERIC_P (subr))
     {
-      if (!*SCM_SUBR_GENERIC (subr))
+      if (!SCM_UNPACK (*SCM_SUBR_GENERIC (subr)))
 	scm_enable_primitive_generic_x (scm_list_1 (subr));
       return *SCM_SUBR_GENERIC (subr);
     }
@@ -1802,7 +1803,7 @@ scm_c_extend_primitive_generic (SCM extended, SCM extension)
   if (goops_loaded_p)
     {
       SCM gf, gext;
-      if (!*SCM_SUBR_GENERIC (extended))
+      if (!SCM_UNPACK (*SCM_SUBR_GENERIC (extended)))
 	scm_enable_primitive_generic_x (scm_list_1 (extended));
       gf = *SCM_SUBR_GENERIC (extended);
       gext = scm_call_2 (SCM_VARIABLE_REF (scm_var_make_extended_generic),
diff --git a/libguile/guardians.c b/libguile/guardians.c
index a341fbfdc..b11bf6430 100644
--- a/libguile/guardians.c
+++ b/libguile/guardians.c
@@ -151,7 +151,7 @@ finalize_guarded (GC_PTR ptr, GC_PTR finalizer_data)
       cell_pool = SCM_CDR (cell_pool);
 
       /* Compute and update G's zombie list.  */
-      SCM_SETCAR (zombies, SCM_PACK (obj));
+      SCM_SETCAR (zombies, obj);
       SCM_SETCDR (zombies, g->zombies);
       g->zombies = zombies;
 
diff --git a/libguile/list.c b/libguile/list.c
index 704151519..221ee79d0 100644
--- a/libguile/list.c
+++ b/libguile/list.c
@@ -35,10 +35,10 @@
 
 /* creating lists */
 
-#define SCM_I_CONS(cell, x, y)			\
-do {						\
-  cell = scm_cell ((scm_t_bits)x, (scm_t_bits)y);			\
-} while (0)
+#define SCM_I_CONS(cell, x, y)                          \
+  do {                                                  \
+    cell = scm_cell (SCM_UNPACK (x), SCM_UNPACK (y));   \
+  } while (0)
 
 SCM
 scm_list_1 (SCM e1)
diff --git a/libguile/macros.c b/libguile/macros.c
index aa6b9cd1c..556e60f57 100644
--- a/libguile/macros.c
+++ b/libguile/macros.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1997,1998,2000,2001,2002,2003, 2006, 2008, 2009, 2010 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,2000,2001,2002,2003, 2006, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -64,9 +64,9 @@ scm_i_make_primitive_macro (const char *name, scm_t_macro_primitive fn)
 {
   SCM z = scm_words (scm_tc16_macro, 5);
   SCM_SET_SMOB_DATA_N (z, 1, (scm_t_bits)fn);
-  SCM_SET_SMOB_DATA_N (z, 2, scm_from_locale_symbol (name));
-  SCM_SET_SMOB_DATA_N (z, 3, SCM_BOOL_F);
-  SCM_SET_SMOB_DATA_N (z, 4, SCM_BOOL_F);
+  SCM_SET_SMOB_OBJECT_N (z, 2, scm_from_locale_symbol (name));
+  SCM_SET_SMOB_OBJECT_N (z, 3, SCM_BOOL_F);
+  SCM_SET_SMOB_OBJECT_N (z, 4, SCM_BOOL_F);
   return z;
 }
 
@@ -104,9 +104,9 @@ SCM_DEFINE (scm_make_syntax_transformer, "make-syntax-transformer", 3, 0, 0,
 
   z = scm_words (scm_tc16_macro, 5);
   SCM_SET_SMOB_DATA_N (z, 1, prim);
-  SCM_SET_SMOB_DATA_N (z, 2, name);
-  SCM_SET_SMOB_DATA_N (z, 3, type);
-  SCM_SET_SMOB_DATA_N (z, 4, binding);
+  SCM_SET_SMOB_OBJECT_N (z, 2, name);
+  SCM_SET_SMOB_OBJECT_N (z, 3, type);
+  SCM_SET_SMOB_OBJECT_N (z, 4, binding);
   return z;
 }
 #undef FUNC_NAME
diff --git a/libguile/memoize.c b/libguile/memoize.c
index 49d294861..0b1aa5194 100644
--- a/libguile/memoize.c
+++ b/libguile/memoize.c
@@ -64,7 +64,8 @@ SCM_SYMBOL (sym_case_lambda_star, "case-lambda*");
 
 scm_t_bits scm_tc16_memoized;
 
-#define MAKMEMO(n, args) 	(scm_cell (scm_tc16_memoized | ((n) << 16), (scm_t_bits)(args)))
+#define MAKMEMO(n, args)                                                \
+  (scm_cell (scm_tc16_memoized | ((n) << 16), SCM_UNPACK (args)))
 
 #define MAKMEMO_BEGIN(exps) \
   MAKMEMO (SCM_M_BEGIN, exps)
@@ -448,13 +449,13 @@ SCM_DEFINE (scm_memoize_expression, "memoize-expression", 1, 0, 0,
 
 #define SCM_MAKE_MEMOIZER(STR, MEMOIZER, N)                             \
   (scm_cell (scm_tc16_memoizer,                                         \
-             (scm_t_bits)(scm_c_make_gsubr (STR, N, 0, 0, MEMOIZER))))
+             SCM_UNPACK (scm_c_make_gsubr (STR, N, 0, 0, MEMOIZER))))
 #define SCM_DEFINE_MEMOIZER(STR, MEMOIZER, N)                           \
 SCM_SNARF_INIT(scm_c_define (STR, SCM_MAKE_MEMOIZER (STR, MEMOIZER, N)))
 
 #define SCM_MAKE_REST_MEMOIZER(STR, MEMOIZER, N)                        \
   (scm_cell (scm_tc16_memoizer,                                         \
-             (scm_t_bits)(scm_c_make_gsubr (STR, N, 0, 1, MEMOIZER))))
+             SCM_UNPACK ((scm_c_make_gsubr (STR, N, 0, 1, MEMOIZER)))))
 #define SCM_DEFINE_REST_MEMOIZER(STR, MEMOIZER, N)                      \
 SCM_SNARF_INIT(scm_c_define (STR, SCM_MAKE_REST_MEMOIZER (STR, MEMOIZER, N)))
 
diff --git a/libguile/modules.c b/libguile/modules.c
index a9fe3b3d9..ca8875dab 100644
--- a/libguile/modules.c
+++ b/libguile/modules.c
@@ -947,7 +947,7 @@ SCM_DEFINE (scm_module_reverse_lookup, "module-reverse-lookup", 2, 0, 0,
 	{
 	  handle = SCM_CAR (ls);
 
-	  if (SCM_CAR (handle) == SCM_PACK (NULL))
+	  if (SCM_UNPACK (SCM_CAR (handle)) == 0)
 	    {
 	      /* FIXME: We hit a weak pair whose car has become unreachable.
 		 We should remove the pair in question or something.  */
diff --git a/libguile/print.c b/libguile/print.c
index b46296abb..4afd12c92 100644
--- a/libguile/print.c
+++ b/libguile/print.c
@@ -525,7 +525,7 @@ iprin1 (SCM exp, SCM port, scm_print_state *pstate)
 	    if (SCM_OBJ_CLASS_FLAGS (exp) & SCM_CLASSF_GOOPS)
 	      {
 		SCM pwps, print = pstate->writingp ? g_write : g_display;
-		if (!print)
+		if (SCM_UNPACK (print) == 0)
 		  goto print_struct;
 		pwps = scm_i_port_with_print_state (port, pstate->handle);
 		pstate->revealed = 1;
diff --git a/libguile/promises.c b/libguile/promises.c
index 45a76a9e5..4aff15092 100644
--- a/libguile/promises.c
+++ b/libguile/promises.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010
+/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010,2011
  * Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
@@ -80,7 +80,7 @@ SCM_DEFINE (scm_make_promise, "make-promise", 1, 0, 0,
   SCM_VALIDATE_THUNK (1, thunk);
   SCM_RETURN_NEWSMOB2 (scm_tc16_promise,
 		       SCM_UNPACK (thunk),
-		       scm_make_recursive_mutex ());
+		       SCM_UNPACK (scm_make_recursive_mutex ()));
 }
 #undef FUNC_NAME
 
diff --git a/libguile/srcprop.c b/libguile/srcprop.c
index f9b000c47..aee0b0985 100644
--- a/libguile/srcprop.c
+++ b/libguile/srcprop.c
@@ -140,8 +140,8 @@ scm_make_srcprops (long line, int col, SCM filename, SCM copy, SCM alist)
   
   SCM_RETURN_NEWSMOB3 (scm_tc16_srcprops,
 		       SRCPROPMAKPOS (line, col),
-		       copy,
-		       alist);
+		       SCM_UNPACK (copy),
+		       SCM_UNPACK (alist));
 }
 
 
diff --git a/libguile/vectors.c b/libguile/vectors.c
index 2ab5b78ea..1cf8f2fc4 100644
--- a/libguile/vectors.c
+++ b/libguile/vectors.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1998,1999,2000,2001, 2006, 2008, 2009, 2010 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1998,1999,2000,2001, 2006, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -213,7 +213,7 @@ scm_c_vector_ref (SCM v, size_t k)
 	scm_out_of_range (NULL, scm_from_size_t (k));
       elt = (SCM_I_VECTOR_ELTS(v))[k];
 
-      if ((elt == SCM_PACK (NULL)) && SCM_I_WVECTP (v))
+      if (SCM_UNPACK (elt) == 0 && SCM_I_WVECTP (v))
 	/* ELT was a weak pointer and got nullified by the GC.  */
 	return SCM_BOOL_F;
 
@@ -232,7 +232,7 @@ scm_c_vector_ref (SCM v, size_t k)
 	  k = SCM_I_ARRAY_BASE (v) + k*dim->inc;
 	  elt = (SCM_I_VECTOR_ELTS (vv))[k];
 
-	  if ((elt == SCM_PACK (NULL)) && (SCM_I_WVECTP (vv)))
+	  if (SCM_UNPACK (elt) == 0 && (SCM_I_WVECTP (vv)))
 	    /* ELT was a weak pointer and got nullified by the GC.  */
 	    return SCM_BOOL_F;
 
diff --git a/libguile/vm-engine.c b/libguile/vm-engine.c
index e449b4372..22bd39c0e 100644
--- a/libguile/vm-engine.c
+++ b/libguile/vm-engine.c
@@ -89,17 +89,17 @@ VM_NAME (SCM vm, SCM program, SCM *argv, int nargs)
 
     /* Initial frame */
     CACHE_REGISTER ();
-    PUSH ((SCM)fp); /* dynamic link */
-    PUSH (0); /* mvra */
-    PUSH ((SCM)ip); /* ra */
+    PUSH (SCM_PACK (fp)); /* dynamic link */
+    PUSH (SCM_PACK (0)); /* mvra */
+    PUSH (SCM_PACK (ip)); /* ra */
     CACHE_PROGRAM ();
     PUSH (program);
     fp = sp + 1;
     ip = SCM_C_OBJCODE_BASE (bp);
     /* MV-call frame, function & arguments */
-    PUSH (0); /* dynamic link */
-    PUSH (0); /* mvra */
-    PUSH (0); /* ra */
+    PUSH (SCM_PACK (0)); /* dynamic link */
+    PUSH (SCM_PACK (0)); /* mvra */
+    PUSH (SCM_PACK (0)); /* ra */
     PUSH (prog);
     if (SCM_UNLIKELY (sp + nargs >= stack_limit))
       goto vm_error_too_many_args;
diff --git a/libguile/vm-i-scheme.c b/libguile/vm-i-scheme.c
index 60e44521e..2d8501253 100644
--- a/libguile/vm-i-scheme.c
+++ b/libguile/vm-i-scheme.c
@@ -168,15 +168,15 @@ VM_DEFINE_INSTRUCTION (144, set_cdr, "set-cdr!", 0, 2, 0)
  */
 
 #undef REL
-#define REL(crel,srel)						\
-{								\
-  ARGS2 (x, y);							\
-  if (SCM_I_INUMP (x) && SCM_I_INUMP (y))			\
-    RETURN (scm_from_bool ((scm_t_signed_bits) (x)		\
-			   crel (scm_t_signed_bits) (y)));	\
-  SYNC_REGISTER ();						\
-  RETURN (srel (x, y));						\
-}
+#define REL(crel,srel)                                                  \
+  {                                                                     \
+    ARGS2 (x, y);                                                       \
+    if (SCM_I_INUMP (x) && SCM_I_INUMP (y))                             \
+      RETURN (scm_from_bool (((scm_t_signed_bits) SCM_UNPACK (x))       \
+                             crel ((scm_t_signed_bits) SCM_UNPACK (y)))); \
+    SYNC_REGISTER ();                                                   \
+    RETURN (srel (x, y));						\
+  }
 
 VM_DEFINE_FUNCTION (145, ee, "ee?", 2)
 {
@@ -297,13 +297,13 @@ VM_DEFINE_FUNCTION (151, add1, "add1", 1)
   ARGS1 (x);
 
   /* Check for overflow.  */
-  if (SCM_LIKELY ((scm_t_intptr) x < INUM_MAX))
+  if (SCM_LIKELY ((scm_t_intptr) SCM_UNPACK (x) < INUM_MAX))
     {
       SCM result;
 
       /* Add the integers without untagging.  */
-      result = SCM_PACK ((scm_t_intptr) x
-			 + (scm_t_intptr) SCM_I_MAKINUM (1)
+      result = SCM_PACK ((scm_t_intptr) SCM_UNPACK (x)
+			 + (scm_t_intptr) SCM_UNPACK (SCM_I_MAKINUM (1))
 			 - scm_tc2_int);
 
       if (SCM_LIKELY (SCM_I_INUMP (result)))
@@ -331,13 +331,13 @@ VM_DEFINE_FUNCTION (153, sub1, "sub1", 1)
   ARGS1 (x);
 
   /* Check for underflow.  */
-  if (SCM_LIKELY ((scm_t_intptr) x > INUM_MIN))
+  if (SCM_LIKELY ((scm_t_intptr) SCM_UNPACK (x) > INUM_MIN))
     {
       SCM result;
 
       /* Substract the integers without untagging.  */
-      result = SCM_PACK ((scm_t_intptr) x
-			 - (scm_t_intptr) SCM_I_MAKINUM (1)
+      result = SCM_PACK ((scm_t_intptr) SCM_UNPACK (x)
+			 - (scm_t_intptr) SCM_UNPACK (SCM_I_MAKINUM (1))
 			 + scm_tc2_int);
 
       if (SCM_LIKELY (SCM_I_INUMP (result)))
diff --git a/libguile/vm-i-system.c b/libguile/vm-i-system.c
index d1ad64fc6..1b4136f3f 100644
--- a/libguile/vm-i-system.c
+++ b/libguile/vm-i-system.c
@@ -765,9 +765,9 @@ VM_DEFINE_INSTRUCTION (52, new_frame, "new-frame", 0, 0, 3)
      know that this frame will point to the current fp: it could be
      placed elsewhere on the stack if captured in a partial
      continuation, and invoked from some other context.  */
-  PUSH (0); /* dynamic link */
-  PUSH (0); /* mvra */
-  PUSH (0); /* ra */
+  PUSH (SCM_PACK (0)); /* dynamic link */
+  PUSH (SCM_PACK (0)); /* mvra */
+  PUSH (SCM_PACK (0)); /* ra */
   NEXT;
 }
 
@@ -1182,9 +1182,9 @@ VM_DEFINE_INSTRUCTION (65, call_cc, "call/cc", 0, 1, 1)
   cont = scm_i_make_continuation (&first, vm, vm_cont);
   if (first) 
     {
-      PUSH (0); /* dynamic link */
-      PUSH (0);  /* mvra */
-      PUSH (0);  /* ra */
+      PUSH (SCM_PACK (0)); /* dynamic link */
+      PUSH (SCM_PACK (0));  /* mvra */
+      PUSH (SCM_PACK (0));  /* ra */
       PUSH (proc);
       PUSH (cont);
       nargs = 1;
diff --git a/libguile/weaks.h b/libguile/weaks.h
index 5cb8bc388..fc16f8bf8 100644
--- a/libguile/weaks.h
+++ b/libguile/weaks.h
@@ -3,7 +3,7 @@
 #ifndef SCM_WEAKS_H
 #define SCM_WEAKS_H
 
-/* Copyright (C) 1995,1996,2000,2001, 2003, 2006, 2008, 2009 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,2000,2001, 2003, 2006, 2008, 2009, 2011 Free Software Foundation, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -50,7 +50,7 @@ SCM_INTERNAL SCM scm_doubly_weak_pair (SCM car, SCM cdr);
 
 /* Testing the weak component(s) of a cell for reachability.  */
 #define SCM_WEAK_PAIR_WORD_DELETED_P(_cell, _word)		\
-  (SCM_CELL_OBJECT ((_cell), (_word)) == SCM_PACK (NULL))
+  (SCM_UNPACK (SCM_CELL_OBJECT ((_cell), (_word))) == 0)
 #define SCM_WEAK_PAIR_CAR_DELETED_P(_cell)	\
   (SCM_WEAK_PAIR_WORD_DELETED_P ((_cell), 0))
 #define SCM_WEAK_PAIR_CDR_DELETED_P(_cell)	\