diff --git a/CMakeLists.txt b/CMakeLists.txt
index 86250e5a6dfab92c94e6355b317f0a258c23a7a8..032b57a88d158ac7a5cfb578633d5c438a14ce7d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -154,8 +154,8 @@ ADD_SUBDIRECTORY(python)
 ADD_SUBDIRECTORY(unittest)
 
 PKG_CONFIG_APPEND_LIBS(${PROJECT_NAME})
-PKG_CONFIG_APPEND_CFLAGS("-isystem ${PYTHON_INCLUDE_DIRS}")
-PKG_CONFIG_APPEND_CFLAGS("-isystem ${NUMPY_INCLUDE_DIRS}")
+PKG_CONFIG_APPEND_CFLAGS("-isystem${PYTHON_INCLUDE_DIRS}")
+PKG_CONFIG_APPEND_CFLAGS("-isystem${NUMPY_INCLUDE_DIRS}")
 PKG_CONFIG_APPEND_BOOST_LIBS(${BOOST_COMPONENTS})
 
 SETUP_PROJECT_FINALIZE()