diff --git a/CMakeLists.txt b/CMakeLists.txt
index f5c4826..43dcdd9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,6 +2,14 @@ cmake_minimum_required (VERSION 2.6)
 project (uts-server)
 include(ExternalProject)
 
+if (CMAKE_VERSION VERSION_LESS "3.1")
+  if (CMAKE_C_COMPILER_ID STREQUAL "GNU")
+    set (CMAKE_C_FLAGS "--std=gnu99 ${CMAKE_C_FLAGS}")
+  endif ()
+else ()
+  set (CMAKE_C_STANDARD 99)
+endif ()
+
 set(VERSION 0.1.8)
 
 option(DEBUG              "compile with debug symbol"    OFF)