diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9eb9e07..cda26a7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
 cmake_minimum_required(VERSION 2.6)
 project(flow_solver)
-set(CMAKE_C_FLAGS "-g -Wall")
+set(CMAKE_C_FLAGS "-g -Wall --std=gnu99")
 add_executable(flow_solver flow_solver.c)