diff --git a/CMakeLists.txt b/CMakeLists.txt
index fbc37fe..54e25f2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -91,7 +91,7 @@ CMAKE_POLICY(SET CMP0026 OLD)
 
 SET(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake) # for FindReadline.cmake
 
-SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -I${PROJECT_SOURCE_DIR}/src")
+SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -I\"${PROJECT_SOURCE_DIR}/src\"")
 
 # external packages
 FIND_PACKAGE( BZip2 )