diff --git a/ChangeLog b/ChangeLog
index 5d36ee129c..25ffe0f9ca 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Feb 16 20:51:17 2013  Kazuki Tsujimoto  <kazuki@callcc.net>
+
+	* vm.c (ENV_IN_HEAP_P): fix off-by-one error.
+
 Sat Feb 16 20:47:16 2013  Akinori MUSHA  <knu@iDaemons.org>
 
 	* configure.in (LIBRUBY_DLDFLAGS): Fix a bug where --with-opt-dir
diff --git a/vm.c b/vm.c
index 3b404984cc..49cc24e2b9 100644
--- a/vm.c
+++ b/vm.c
@@ -262,7 +262,7 @@ ruby_vm_run_at_exit_hooks(rb_vm_t *vm)
  */
 
 #define ENV_IN_HEAP_P(th, env)  \
-  (!((th)->stack < (env) && (env) < ((th)->stack + (th)->stack_size)))
+  (!((th)->stack <= (env) && (env) < ((th)->stack + (th)->stack_size)))
 #define ENV_VAL(env)        ((env)[1])
 
 static void