--- malloc/hooks.c~	2009-06-08 17:55:07.982329000 +0200
+++ malloc/hooks.c	2009-06-08 17:56:41.178045000 +0200
@@ -276,15 +276,18 @@
   mchunkptr p;
 
   if(!mem) return;
+#ifndef ATOMIC_FASTBINS
+  (void)mutex_lock(&main_arena.mutex);
+#endif
   p = mem2chunk_check(mem, NULL);
   if(!p) {
     malloc_printerr(check_action, "free(): invalid pointer", mem);
-    return;
+    goto out;
   }
 #if HAVE_MMAP
   if (chunk_is_mmapped(p)) {
     munmap_chunk(p);
-    return;
+    goto out;
   }
 #endif
 #if 0 /* Erase freed memory. */
@@ -293,8 +296,12 @@
 #ifdef ATOMIC_FASTBINS
   _int_free(&main_arena, p, 0);
 #else
-  (void)mutex_lock(&main_arena.mutex);
   _int_free(&main_arena, p);
+#endif
+out:
+#ifdef ATOMIC_FASTBINS
+  ;
+#else
   (void)mutex_unlock(&main_arena.mutex);
 #endif
 }