diff --git a/ChangeLog b/ChangeLog
index 01f9280364..2938126075 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Mar 19 22:12:46 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* gc.c (rb_copy_wb_protected_attribute): `dest' can be WB unprotected.
+
 Thu Mar 19 21:25:25 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* gc.c (rb_copy_wb_protected_attribute): demote `dest' object.
diff --git a/gc.c b/gc.c
index 2a191ae90e..a0158d24db 100644
--- a/gc.c
+++ b/gc.c
@@ -5734,12 +5734,7 @@ rb_copy_wb_protected_attribute(VALUE dest, VALUE obj)
 #if USE_RGENGC
     rb_objspace_t *objspace = &rb_objspace;
 
-    if (RGENGC_CHECK_MODE > 0 && RVALUE_WB_UNPROTECTED(dest)) {
-	rb_bug("rb_copy_wb_protected_attribute: dest should not be WB unprotected - %s",
-	       obj_info(dest));
-    }
-
-    if (RVALUE_WB_UNPROTECTED(obj)) {
+    if (RVALUE_WB_UNPROTECTED(obj) && !RVALUE_WB_UNPROTECTED(dest)) {
 	if (!RVALUE_OLD_P(dest)) {
 	    MARK_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(dest), dest);
 	    RVALUE_AGE_RESET_RAW(dest);