diff --git a/ChangeLog b/ChangeLog
index 12c2283032..649ad915af 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Nov  6 09:13:32 2013  Koichi Sasada  <ko1@atdot.net>
+
+	* gc.c: define RGENGC_ESTIMATE_OLDSPACE == 0 if USE_RGENGC is 0.
+
 Wed Nov  6 07:13:18 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* gc.c (Init_GC): add GC::OPTS to show options.
diff --git a/gc.c b/gc.c
index 9583ec1715..7b4ae45343 100644
--- a/gc.c
+++ b/gc.c
@@ -194,11 +194,14 @@ static ruby_gc_params_t initial_params = {
 #endif
 
 #else /* USE_RGENGC */
+
 #define RGENGC_DEBUG       0
 #define RGENGC_CHECK_MODE  0
 #define RGENGC_PROFILE     0
 #define RGENGC_THREEGEN    0
-#endif
+#define RGENGC_ESTIMATE_OLDSPACE 0
+
+#endif /* USE_RGENGC */
 
 #ifndef GC_PROFILE_MORE_DETAIL
 #define GC_PROFILE_MORE_DETAIL 0