diff --git a/ChangeLog b/ChangeLog
index 6929c73e70..bcbb582984 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jun 13 14:18:54 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* gc.c (ruby_stack_check): STACK_LENGTH should be less than
+	  STACK_LEVEL_MAX.
+
 Fri Jun 13 12:55:37 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* enum.c (sort_by_i): use NODE_DOT2 instead of NODE_MEMO to avoid
diff --git a/gc.c b/gc.c
index 25a2016c53..567dca1cf8 100644
--- a/gc.c
+++ b/gc.c
@@ -236,7 +236,6 @@ rb_objspace_alloc(void)
 /*#define HEAP_SIZE 0x800 */
 
 #define HEAP_OBJ_LIMIT (HEAP_SIZE / sizeof(struct RVALUE))
-#define FREE_MIN  4096
 
 extern st_table *rb_class_tbl;
 VALUE *rb_gc_stack_start = 0;
@@ -818,11 +817,11 @@ ruby_stack_check(void)
     int ret;
     rb_thread_t *th = GET_THREAD();
     SET_STACK_END;
-    ret = STACK_LENGTH > STACK_LEVEL_MAX + GC_WATER_MARK;
+    ret = STACK_LENGTH > STACK_LEVEL_MAX - GC_WATER_MARK;
 #ifdef __ia64
     if (!ret) {
         ret = (VALUE*)rb_ia64_bsp() - th->machine_register_stack_start >
-              th->machine_register_stack_maxsize/sizeof(VALUE) + GC_WATER_MARK;
+              th->machine_register_stack_maxsize/sizeof(VALUE) - GC_WATER_MARK;
     }
 #endif
     return ret;