diff --git a/python/CMakeLists.txt b/python/CMakeLists.txt
index 0e67f2f..6045aca 100644
--- a/python/CMakeLists.txt
+++ b/python/CMakeLists.txt
@@ -88,11 +88,13 @@ message(STATUS "User python site: ${USER_PYTHON_SITE_PACKAGES}")
 
 OPTION(INSTALL_PYTHON_LOCAL OFF)
 
-IF (NOT INSTALL_PYTHON_LOCAL)
-  SET(PYTHON_SITE_PACKAGES ${SYSTEM_PYTHON_SITE_PACKAGES})
-ELSE (NOT INSTALL_PYTHON_LOCAL)
-  SET(PYTHON_SITE_PACKAGES ${USER_PYTHON_SITE_PACKAGES})
-ENDIF(NOT INSTALL_PYTHON_LOCAL)
+IF (NOT PYTHON_SITE_PACKAGES)
+  IF (NOT INSTALL_PYTHON_LOCAL)
+    SET(PYTHON_SITE_PACKAGES ${SYSTEM_PYTHON_SITE_PACKAGES})
+  ELSE (NOT INSTALL_PYTHON_LOCAL)
+    SET(PYTHON_SITE_PACKAGES ${USER_PYTHON_SITE_PACKAGES})
+  ENDIF(NOT INSTALL_PYTHON_LOCAL)
+ENDIF()
 cmessage(STATUS "Python install location: ${PYTHON_SITE_PACKAGES}")