diff --git a/test/unittest/CMakeLists.txt b/test/unittest/CMakeLists.txt
index 072b7b1..fc8803e 100644
--- a/test/unittest/CMakeLists.txt
+++ b/test/unittest/CMakeLists.txt
@@ -3,6 +3,7 @@ include(CheckCXXCompilerFlag)
 set(UNITTEST_SOURCES
 	allocatorstest.cpp
     bigintegertest.cpp
+    clzlltest.cpp
 	cursorstreamwrappertest.cpp
     documenttest.cpp
     dtoatest.cpp
diff --git a/test/unittest/clzlltest.cpp b/test/unittest/clzlltest.cpp
new file mode 100644
index 0000000..9c52812
--- /dev/null
+++ b/test/unittest/clzlltest.cpp
@@ -0,0 +1,34 @@
+// Tencent is pleased to support the open source community by making RapidJSON available.
+// 
+// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
+//
+// Licensed under the MIT License (the "License"); you may not use this file except
+// in compliance with the License. You may obtain a copy of the License at
+//
+// http://opensource.org/licenses/MIT
+//
+// 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.
+
+#include "unittest.h"
+#include "rapidjson/internal/clzll.h"
+
+#ifdef __GNUC__
+RAPIDJSON_DIAG_PUSH
+#endif
+
+using namespace rapidjson::internal;
+
+TEST(clzll, normal) {
+    EXPECT_EQ(clzll(1), 0U);
+    EXPECT_EQ(clzll(2), 1U);
+    EXPECT_EQ(clzll(12), 3U);
+    EXPECT_EQ(clzll(0x0000000080000001UL), 31U);
+    EXPECT_EQ(clzll(0x8000000000000001UL), 63U);
+}
+
+#ifdef __GNUC__
+RAPIDJSON_DIAG_POP
+#endif