diff --git a/CMakeLists.txt b/CMakeLists.txt
index f570c11..4d02f5c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -45,7 +45,7 @@ endif (FORCE_OPENGLES OR RASPBERRY_PI)
 
 if (WITH_BUILTIN_PHYSFS)
 	message(STATUS "Using internal PhysFS")
-	set(PHYSFS_INCLUDE_DIR "lib/physfs-2.0.3")
+	set(PHYSFS_INCLUDE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/lib/physfs-2.0.3")
 	set(PHYSFS_LIBRARY "physfs")
 else(WITH_BUILTIN_PHYSFS)
 	message(STATUS "Using system's PhysFS, set WITH_BUILTIN_PHYSFS to on to override this")