diff --git a/associate.m b/associate.m
index 2289dca..0343363 100644
--- a/associate.m
+++ b/associate.m
@@ -361,7 +361,7 @@ PRIVATE void gc_setTypeForClass(Class cls, void *type)
 
 int objc_sync_enter(id object)
 {
-	if (isSmallObject(object)) { return 0; }
+	if ((object == 0) || isSmallObject(object)) { return 0; }
 	struct reference_list *list = referenceListForObject(object, YES);
 	LOCK(&list->lock);
 	return 0;
@@ -369,7 +369,7 @@ int objc_sync_enter(id object)
 
 int objc_sync_exit(id object)
 {
-	if (isSmallObject(object)) { return 0; }
+	if ((object == 0) || isSmallObject(object)) { return 0; }
 	struct reference_list *list = referenceListForObject(object, NO);
 	if (NULL != list)
 	{