diff --git a/ChangeLog b/ChangeLog
index 3f33e36f27..fd4ffa4471 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,8 @@
-Sat Mar 31 07:44:30 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Sat Mar 31 07:47:31 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* hash.c (st_foreach_safe): since table is not for VALUE, Qundef is
+	  not special value, so use 0 instead.  therefore this function can be
+	  applied to only st_table which 0 is invalid as keys, e.g., IDs.
 
 	* hash.c: Qundef cannot be passed from st_foreach_check().
 
diff --git a/hash.c b/hash.c
index 328917862c..b036e8bf8a 100644
--- a/hash.c
+++ b/hash.c
@@ -131,7 +131,7 @@ st_foreach_safe(st_table *table, int (*func)(ANYARGS), st_data_t a)
     arg.tbl = table;
     arg.func = (st_foreach_func *)func;
     arg.arg = a;
-    if (st_foreach_check(table, foreach_safe_i, (st_data_t)&arg, (st_data_t)Qundef)) {
+    if (st_foreach_check(table, foreach_safe_i, (st_data_t)&arg, 0)) {
 	rb_raise(rb_eRuntimeError, "hash modified during iteration");
     }
 }