diff --git a/ChangeLog b/ChangeLog
index 1315ad83f3..19c5db0273 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Nov  6 23:55:18 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* string.c (sym_printable): QUOTE() should not raise an exception
+	  even on invalid byte sequence.
+
 Thu Nov  6 21:44:36 2014  Tanaka Akira  <akr@fsij.org>
 
 	* test/test_unicode_normalize.rb: Rename TestNormalize to
diff --git a/string.c b/string.c
index 5c87424d18..84481dfe8c 100644
--- a/string.c
+++ b/string.c
@@ -8497,8 +8497,11 @@ sym_printable(const char *s, const char *send, rb_encoding *enc)
 {
     while (s < send) {
 	int n;
-	int c = rb_enc_codepoint_len(s, send, &n, enc);
+	int c = rb_enc_precise_mbclen(s, send, enc);
 
+	if (!MBCLEN_CHARFOUND_P(c)) return FALSE;
+	n = MBCLEN_CHARFOUND_LEN(c);
+	c = rb_enc_mbc_to_codepoint(s, send, enc);
 	if (!rb_enc_isprint(c, enc)) return FALSE;
 	s += n;
     }