diff --git a/ChangeLog b/ChangeLog
index 89492428ac..2da3db02d1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Sep 15 14:34:32 2008  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* encoding.c (RUBY_MAX_CHAR_LEN): defined.
+
+	* encoding.c (str_cat_char): use RUBY_MAX_CHAR_LEN.
+
 Mon Sep 15 13:53:33 2008  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* encoding.c (rb_enc_compatible): accepst other than strings and
diff --git a/string.c b/string.c
index dd61d52da7..843d770cd0 100644
--- a/string.c
+++ b/string.c
@@ -43,6 +43,7 @@
 VALUE rb_cString;
 VALUE rb_cSymbol;
 
+#define RUBY_MAX_CHAR_LEN 16
 #define STR_TMPLOCK FL_USER7
 #define STR_NOEMBED FL_USER1
 #define STR_SHARED  FL_USER2 /* = ELTS_SHARED */
@@ -3790,7 +3791,7 @@ rb_str_to_s(VALUE str)
 static void
 str_cat_char(VALUE str, int c, rb_encoding *enc)
 {
-    char s[16];
+    char s[RUBY_MAX_CHAR_LEN];
     int n = rb_enc_codelen(c, enc);
 
     rb_enc_mbcput(c, s, enc);