diff --git a/libguile/throw.c b/libguile/throw.c
index 051f6d382..fd08e6e70 100644
--- a/libguile/throw.c
+++ b/libguile/throw.c
@@ -54,16 +54,14 @@ static scm_t_bits tc16_jmpbuffer;
 
 #define SCM_JMPBUFP(OBJ)	SCM_TYP16_PREDICATE (tc16_jmpbuffer, OBJ)
 
-#define JBACTIVE(OBJ)		(SCM_CELL_WORD_0 (OBJ) & (1L << 16L))
-#define ACTIVATEJB(x)	\
-  (SCM_SET_CELL_WORD_0 ((x), (SCM_CELL_WORD_0 (x) | (1L << 16L))))
-#define DEACTIVATEJB(x) \
-  (SCM_SET_CELL_WORD_0 ((x), (SCM_CELL_WORD_0 (x) & ~(1L << 16L))))
+#define JBACTIVE(OBJ)		(SCM_SMOB_FLAGS (OBJ) & 1L)
+#define ACTIVATEJB(x)		(SCM_SET_SMOB_FLAGS ((x), 1L))
+#define DEACTIVATEJB(x)		(SCM_SET_SMOB_FLAGS ((x), 0L))
 
-#define JBJMPBUF(OBJ)           ((scm_i_jmp_buf *) SCM_CELL_WORD_1 (OBJ))
-#define SETJBJMPBUF(x, v)        (SCM_SET_CELL_WORD_1 ((x), (scm_t_bits) (v)))
-#define SCM_JBPREUNWIND(x)      ((struct pre_unwind_data *) SCM_CELL_WORD_3 (x))
-#define SCM_SETJBPREUNWIND(x, v) (SCM_SET_CELL_WORD_3 ((x), (scm_t_bits) (v)))
+#define JBJMPBUF(OBJ)           ((scm_i_jmp_buf *) SCM_SMOB_DATA_1 (OBJ))
+#define SETJBJMPBUF(x, v)        (SCM_SET_SMOB_DATA_1 ((x), (scm_t_bits) (v)))
+#define SCM_JBPREUNWIND(x)      ((struct pre_unwind_data *) SCM_SMOB_DATA_3 (x))
+#define SCM_SETJBPREUNWIND(x, v) (SCM_SET_SMOB_DATA_3 ((x), (scm_t_bits) (v)))
 
 static int
 jmpbuffer_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
@@ -269,7 +267,7 @@ static scm_t_bits tc16_pre_unwind_data;
 static int
 pre_unwind_data_print (SCM closure, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
-  struct pre_unwind_data *c = (struct pre_unwind_data *) SCM_CELL_WORD_1 (closure);
+  struct pre_unwind_data *c = (struct pre_unwind_data *) SCM_SMOB_DATA_1 (closure);
   char buf[200];
 
   sprintf (buf, "#<pre-unwind-data 0x%lx 0x%lx>",
@@ -783,7 +781,7 @@ scm_ithrow (SCM key, SCM args, int noreturn SCM_UNUSED)
 	      else
 		{
 		  struct pre_unwind_data *c =
-		    (struct pre_unwind_data *) SCM_CELL_WORD_1 (jmpbuf);
+		    (struct pre_unwind_data *) SCM_SMOB_DATA_1 (jmpbuf);
 		  if (!c->running)
 		    break;
 		}
@@ -816,7 +814,7 @@ scm_ithrow (SCM key, SCM args, int noreturn SCM_UNUSED)
   if (SCM_PRE_UNWIND_DATA_P (jmpbuf))
     {
       struct pre_unwind_data *c =
-	(struct pre_unwind_data *) SCM_CELL_WORD_1 (jmpbuf);
+	(struct pre_unwind_data *) SCM_SMOB_DATA_1 (jmpbuf);
       SCM handle, answer;
 
       /* For old-style lazy-catch behaviour, we unwind the dynamic