1 files changed, 5 insertions, 5 deletions
diff --git a/sprintf.c b/sprintf.c
index 705d3cece5..5c0f94005c 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -605,11 +605,11 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
 		}
 		CHECKNAMEARG(start, len, enc);
 		get_hash(&hash, argc, argv);
-		sym = rb_check_symbol_cstr(start + 1,
-					   len - 2 /* without parenthesis */,
-					   enc);
-		if (sym != Qnil) nextvalue = rb_hash_lookup2(hash, sym, Qundef);
-		if (nextvalue == Qundef) {
+		sym = rb_cstr_intern(start + 1,
+				     len - 2 /* without parenthesis */,
+				     enc);
+		nextvalue = rb_hash_aref(hash, sym);
+		if (NIL_P(nextvalue) && !FL_TEST(hash, HASH_PROC_DEFAULT)) {
 		    rb_enc_raise(enc, rb_eKeyError, "key%.*s not found", len, start);
 		}
 		if (term == '}') goto format_s;