diff --git a/CMakeLists.txt b/CMakeLists.txt
index ec140245f0..0c207d17d6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -170,6 +170,7 @@ string(REGEX MATCH "Clang" CMAKE_COMPILER_IS_CLANG "${CMAKE_C_COMPILER_ID}")
 
 include(CheckCCompilerFlag)
 
+set(CMAKE_C_EXTENSIONS OFF)
 set(CMAKE_C_STANDARD 99)
 
 if(CMAKE_COMPILER_IS_GNU)