diff --git a/CMakeLists.txt b/CMakeLists.txt
index f5fc715..f218e21 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,7 +21,7 @@
     set(CMAKE_BUILD_TYPE debug)
 endif()
 
-set(CMAKE_C_FLAGS         "${CMAKE_C_FLAGS} -Wall -Wextra")
+set(CMAKE_C_FLAGS         "${CMAKE_C_FLAGS} -Wall -Wextra -std=c89")
 set(CMAKE_C_FLAGS_RELEASE "-O2 -DNDEBUG")
 set(CMAKE_C_FLAGS_PACKAGE "-g -O2 -DNDEBUG")
 set(CMAKE_C_FLAGS_DEBUG   "-g -O0")