diff --git a/ChangeLog b/ChangeLog
index 0f83d62b43..2e3a87b973 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sat Sep 10 08:30:03 2011  Koichi Sasada  <ko1@atdot.net>
+
+	* gc.c (GC_PROFILE_MORE_DETAIL, CALC_EXACT_MALLOC_SIZE):
+	  define macros only if they are not defined.
+	  fixes: [Ruby 1.9 - Feature #5291]
+
 Sat Sep 10 08:25:47 2011  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* parse.y (bv_decls): parse.y relies on $$ = $1 before action
diff --git a/gc.c b/gc.c
index f0d74c9c31..48a1db32d5 100644
--- a/gc.c
+++ b/gc.c
@@ -93,7 +93,10 @@ static unsigned int initial_free_min       = FREE_MIN;
 int ruby_gc_debug_indent = 0;
 
 /* for GC profile */
+#ifndef GC_PROFILE_MORE_DETAIL
 #define GC_PROFILE_MORE_DETAIL 0
+#endif
+
 typedef struct gc_profile_record {
     double gc_time;
     double gc_mark_time;
@@ -309,7 +312,9 @@ struct gc_list {
     struct gc_list *next;
 };
 
+#ifndef CALC_EXACT_MALLOC_SIZE
 #define CALC_EXACT_MALLOC_SIZE 0
+#endif
 
 typedef struct rb_objspace {
     struct {