diff --git a/ChangeLog b/ChangeLog
index e9076a959d..0cb42a9fc3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -14,6 +14,9 @@ Sat Dec 13 15:52:27 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 	* string.c (sym_equal): remove documentation error "Otherwise,
 	  compares them as strings".  [ruby-dev:37398]
 
+	* string.c (sym_inspect): quote if symbol contains non-printable
+	  characters.  [ruby-dev:37398]
+
 Sat Dec 13 14:24:38 2008  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
 
 	* test/ruby/enc/test_utf16.rb: feature changed in r20626.
diff --git a/string.c b/string.c
index c34abb4375..8b16d5eb12 100644
--- a/string.c
+++ b/string.c
@@ -6826,6 +6826,19 @@ sym_equal(VALUE sym1, VALUE sym2)
 }
 
 
+static int
+sym_printable(const char *s, rb_encoding *enc)
+{
+    const char *send = s + strlen(s);
+    while (s) {
+	int c = rb_enc_codepoint(s, send, enc);
+	int n = rb_enc_codelen(c, enc);
+	if (!rb_enc_isprint(c, enc)) return Qfalse;
+	s += n;
+    }
+    return Qtrue;
+}
+
 /*
  *  call-seq:
  *     sym.inspect    => string
@@ -6848,7 +6861,8 @@ sym_inspect(VALUE sym)
     RSTRING_PTR(str)[0] = ':';
     memcpy(RSTRING_PTR(str)+1, RSTRING_PTR(sym), RSTRING_LEN(sym));
     if (RSTRING_LEN(sym) != strlen(RSTRING_PTR(sym)) ||
-	!rb_enc_symname_p(RSTRING_PTR(sym), enc)) {
+	!rb_enc_symname_p(RSTRING_PTR(sym), enc) ||
+	!sym_printable(RSTRING_PTR(sym), enc)) {
 	str = rb_str_inspect(str);
 	strncpy(RSTRING_PTR(str), ":\"", 2);
     }