Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -589,7 +589,7 @@ IF(ENABLE_GPS)
      ADD_DEFINITIONS(-DENABLE_GPS)
      IF(WIN32)
           SET(ENABLE_LIBGPS 0)
-     ELSE(WIN32)
+     ELSEIF(NOT DEFINED ENABLE_LIBGPS)
           FIND_PACKAGE(GPS QUIET)
           IF(GPS_FOUND)
                IF(${GPS_VERSION_STRING} VERSION_LESS MINIMAL_GPS_API_VERSION)
