1 files changed, 1 insertions, 1 deletions
diff --git a/gc.c b/gc.c
index db3dce55bf..1eaa3d066b 100644
--- a/gc.c
+++ b/gc.c
@@ -1176,7 +1176,7 @@ rb_data_typed_object_alloc(VALUE klass, void *datap, const rb_data_type_t *type)
 size_t
 rb_objspace_data_type_memsize(VALUE obj)
 {
-    if (RTYPEDDATA_P(obj)) {
+    if (RTYPEDDATA_P(obj) && RTYPEDDATA_TYPE(obj)->function.dsize) {
 	return RTYPEDDATA_TYPE(obj)->function.dsize(RTYPEDDATA_DATA(obj));
     }
     else {