diff --git a/src/runtime/GlobalObjectBuiltinIntl.cpp b/src/runtime/GlobalObjectBuiltinIntl.cpp
index 6e29d67b6..70d8d7798 100644
--- a/src/runtime/GlobalObjectBuiltinIntl.cpp
+++ b/src/runtime/GlobalObjectBuiltinIntl.cpp
@@ -775,7 +775,7 @@ static IntlMatcherResult lookupMatcher(ExecutionState& state, const Vector<Strin
             size_t extensionIndex = locale->find(String::fromASCII("-u-"));
             RELEASE_ASSERT(extensionIndex != SIZE_MAX);
 
-            size_t extensionLength = locale->length() - extensionIndex;
+            size_t extensionLength = locale->length();
             size_t end = extensionIndex + 3;
             while (end < locale->length()) {
                 end = locale->find(String::fromASCII("-"), end);
diff --git a/test/regression-tests/issue-237.js b/test/regression-tests/issue-237.js
new file mode 100644
index 000000000..858b2eba4
--- /dev/null
+++ b/test/regression-tests/issue-237.js
@@ -0,0 +1,20 @@
+/* Copyright 2019-present Samsung Electronics Co., Ltd. and other contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+Intl.NumberFormat('en-u-foo-U-foo')