diff --git a/modules/src/malloc/log.h b/modules/src/malloc/log.h
index d1d8929a2..a15c7b523 100644
--- a/modules/src/malloc/log.h
+++ b/modules/src/malloc/log.h
@@ -10,8 +10,20 @@
 public link_free_chunk(), unlink_free_chunk();
 public mallink *first_present(), *search_free_list();
 
+#ifdef STORE
+#define in_store(ml)		((size_type)_log_prev_of(ml) & 01)
+#define set_store(ml, e) \
+	(_log_prev_of(ml) = (mallink *) \
+		((e) ? (size_type) _log_prev_of(ml) | 01 : \
+		       (size_type) _log_prev_of(ml) & ~01))
+#define log_prev_of(ml)		(mallink *)((size_type)_log_prev_of(ml) & ~01)
+#define set_log_prev(ml,e) \
+	(_log_prev_of(ml) = (mallink *)((char *)e + in_store(ml)))
+#else
 #define	set_log_prev(ml,e)	(_log_prev_of(ml) = (e))
 #define	log_prev_of(ml)		(mallink *) (_log_prev_of(ml))
+#endif
 
 #define	set_log_next(ml,e)	(_log_next_of(ml) = (e))
 #define	log_next_of(ml)		(mallink *) (_log_next_of(ml))
+
diff --git a/modules/src/malloc/mal.c b/modules/src/malloc/mal.c
index 3c602d596..67b5356ca 100644
--- a/modules/src/malloc/mal.c
+++ b/modules/src/malloc/mal.c
@@ -26,11 +26,11 @@
 #define	ILL_BREAK		(char *)(-1)	/* funny failure value */
 #endif
 extern char *SBRK();
+privatedata char *freed;
 #ifdef STORE
 #define	MAX_STORE	32
 private do_free(), Xfree(), sell_out();
 privatedata mallink *store[MAX_STORE];
-privatedata char *freed;
 #endif STORE
 
 char *
@@ -49,6 +49,7 @@ malloc(n)
 		
 		if (ml = *stp)	{
 			*stp = log_next_of(ml);
+			set_store(ml, 0);
 			check_mallinks("malloc fast exit");
 			return block_of_mallink(ml);
 		}
@@ -152,7 +153,7 @@ Xfree()
 #ifdef STORE
 
 	freed = 0;
-	if (free_of(ml))
+	if (free_of(ml) || in_store(ml))
 		return;				/* user frees free block */
 	if (size_of(ml) <= MAX_STORE*MIN_SIZE)	{
 		/* return to store */
@@ -160,6 +161,7 @@ Xfree()
 		
 		set_log_next(ml, *stp);
 		*stp = ml;
+		set_store(ml, 1);
 		check_mallinks("free fast exit");
 	}
 	else	{
@@ -283,6 +285,7 @@ sell_out()	{
 		
 		while (ml)	{
 			*stp = log_next_of(ml);
+			set_store(ml, 0);
 			do_free(ml);
 			ml = *stp;
 		}