diff --git a/CMakeLists.txt b/CMakeLists.txt
index cc0935b..9f316c9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,7 +23,7 @@ find_package(Jemalloc REQUIRED)
 
 set(LIBS ${LIBS} ${PCRE_LIBRARIES} ${Jemalloc_LIBRARIES} r3)
 
-set (CMAKE_CFLAGS "-Wall -pipe -g3 -funroll-loops")
+set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99 -Wall -pipe -g3 -funroll-loops")
 # set (CMAKE_CXX_FLAGS "-std=c++0x -arch x86_64 -stdlib=libc++ -g3 -Wall -O0")
 enable_testing()
 
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 02bbdda..6b61a8d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -4,7 +4,8 @@ include_directories("${PROJECT_SOURCE_DIR}/include")
 # install(TARGETS swiftnav-static DESTINATION lib${LIB_SUFFIX})
 
 set(R3_SRCS node.c str.c list.c token.c edge.c)
-set(CMAKE_CFLAGS "-Wall -pipe -g3 -funroll-loops")
+set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99 -Wall -pipe -g3 -funroll-loops")
+
 # set(LIBS ${LIBS} ${PCRE_LIBRARIES} ${Judy_LIBRARIES} ${Jemalloc_LIBRARIES} r3)
 set(LIBS ${LIBS} ${PCRE_LIBRARIES} ${Jemalloc_LIBRARIES} r3)