diff --git a/ChangeLog b/ChangeLog
index 3d76091029..22a59c767a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri May 11 14:09:47 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/bigdecimal/bigdecimal.c (PUSH): to prevent VALUE from GC,
+	  must not cast it to unsigned long, which may be shorter than
+	  VALUE, and the result can be mere garbage.
+
 Fri May 11 09:51:07 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/test/unit.rb (Test::Unit::Runner#failed): no unnecessary
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index a2d705ce20..e5f8545991 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -61,7 +61,7 @@ static ID id_eq;
 
 /* MACRO's to guard objects from GC by keeping them in stack */
 #define ENTER(n) volatile VALUE vStack[n];int iStack=0
-#define PUSH(x)  vStack[iStack++] = (unsigned long)(x);
+#define PUSH(x)  vStack[iStack++] = (VALUE)(x);
 #define SAVE(p)  PUSH(p->obj);
 #define GUARD_OBJ(p,y) {p=y;SAVE(p);}