diff --git a/ChangeLog b/ChangeLog
index 6072b53c3d..6847a87295 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Sat Jun  8 15:58:18 2013  Tanaka Akira  <akr@fsij.org>
+
+	* random.c (rand_init): Add a cast to fix clang compile error:
+	  random.c:410:32: error: implicit conversion loses integer precision:
+	  'size_t' (aka 'unsigned long') to 'int' [-Werror,-Wshorten-64-to-32]
+	  This cast doesn't cause a problem because len is not bigger than
+	  MT_MAX_STATE.
+
 Sat Jun  8 15:30:03 2013  Tanaka Akira  <akr@fsij.org>
 
 	* random.c (rand_init): Use rb_integer_pack.
diff --git a/random.c b/random.c
index 19b65a7083..38aee0833d 100644
--- a/random.c
+++ b/random.c
@@ -407,7 +407,7 @@ rand_init(struct MT *mt, VALUE vseed)
     else {
         if (sign != 2 && buf[len-1] == 1) /* remove leading-zero-guard */
             len--;
-        init_by_array(mt, buf, len);
+        init_by_array(mt, buf, (int)len);
     }
     if (buf != buf0) xfree(buf);
     return seed;