diff --git a/ChangeLog b/ChangeLog
index 75f3be9341..ef333bcb92 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jun  8 23:09:51 2016  Kazuhiro NISHIYAMA  <zn@mbf.nifty.com>
+
+	* string.c (rb_str_ascii_casemap): fix compile error.
+
 Wed Jun  8 22:22:24 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* string.c: Revert previous commit (possibility of endless loop).
diff --git a/string.c b/string.c
index e1cedf42aa..776a4d32ae 100644
--- a/string.c
+++ b/string.c
@@ -5837,7 +5837,7 @@ static void
 rb_str_ascii_casemap(VALUE source, OnigCaseFoldType *flags, rb_encoding *enc)
 {
     OnigUChar *source_current, *source_end;
-    int old_length = RSTRING_LEN(source);
+    long old_length = RSTRING_LEN(source);
     int length_or_invalid;
 
     if (old_length == 0) return;