diff --git a/ChangeLog b/ChangeLog
index 188138d7a3..16bf7d5188 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Mon Feb  1 17:11:12 2010  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
+
+	* string (rb_string_value): warning for implicit conversion
+	  from Symbol to String. This behavior was introduced in r22606,
+	  merged in r22738 to ruby_1_9_1. It was an unexpected language
+	  feature change. It will be removed from Ruby in the 1.9.2.
+	  c.f. [ruby-dev:40274].
+
 Thu Feb 26 13:23:20 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* iseq.c (cdhash_each): resurrects internal literals.
diff --git a/string.c b/string.c
index 8a8835eca5..125599c24a 100644
--- a/string.c
+++ b/string.c
@@ -1242,6 +1242,7 @@ rb_string_value(volatile VALUE *ptr)
     VALUE s = *ptr;
     if (TYPE(s) != T_STRING) {
 	if (SYMBOL_P(s)) {
+            rb_warn("Implicit conversion from Symbol to String was introduced by mistake. This bug will be fixed in Ruby 1.9.2.");
 	    s = rb_sym_to_s(s);
 	}
 	else {