diff --git a/ChangeLog b/ChangeLog
index a895ba365d..406e275a57 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Sep  2 07:02:10 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (Init_Bignum): Define Bignum::GMP_VERSION when GMP is used.
+
 Mon Sep  2 01:46:14 2013  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (big2str_generic): Reduce arguments.
diff --git a/bignum.c b/bignum.c
index 32842ba36c..9bebf7224a 100644
--- a/bignum.c
+++ b/bignum.c
@@ -6752,5 +6752,9 @@ Init_Bignum(void)
     rb_define_method(rb_cBignum, "odd?", rb_big_odd_p, 0);
     rb_define_method(rb_cBignum, "even?", rb_big_even_p, 0);
 
+#ifdef USE_GMP
+    rb_define_const(rb_cBignum, "GMP_VERSION", rb_sprintf("GMP %s", gmp_version));
+#endif
+
     power_cache_init();
 }