diff --git a/ChangeLog b/ChangeLog
index 55d1ec50d6..4388ac460d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Jun 10 00:25:03 2011  CHIKANAGA Tomoyuki  <nagachika00@gmail.com>
+
+	* gc.c: remove an unused declaration.
+
 Fri Jun 10 00:24:04 2011  Tadayoshi Funaba  <tadf@dotrb.org>
 
 	* rational.c (string_to_r): Rational#** may return flonum.
diff --git a/gc.c b/gc.c
index aab0963c29..f8e2513ff4 100644
--- a/gc.c
+++ b/gc.c
@@ -491,7 +491,6 @@ rb_objspace_free(rb_objspace_t *objspace)
 
 #define HEAP_OBJ_LIMIT (HEAP_SIZE / sizeof(struct RVALUE))
 
-extern VALUE rb_cMutex;
 extern st_table *rb_class_tbl;
 
 int ruby_disable_gc_stress = 0;