diff --git a/ChangeLog b/ChangeLog
index f583deadc7..85b577d2dd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Tue Dec  8 23:05:47 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* compile.c (iseq_ibf_dump): fix for clang type checker.
+
 Tue Dec  8 23:04:02 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* iseq.c (iseq_s_load): fix mysterious bug.
diff --git a/compile.c b/compile.c
index bd1497823d..fd0af93c76 100644
--- a/compile.c
+++ b/compile.c
@@ -8062,7 +8062,7 @@ iseq_ibf_dump(const rb_iseq_t *iseq, VALUE opt)
 
     if (RTEST(opt)) {
 	VALUE opt_str = rb_check_string_type(opt);
-	header.extra_size = RSTRING_LEN(opt_str) + 1;
+	header.extra_size = (unsigned int)RSTRING_LEN(opt_str) + 1;
 	ibf_dump_write(&dump, RSTRING_PTR(opt_str), header.extra_size);
     }
     else {