diff --git a/Engine/lib/sdl/CMakeLists.txt b/Engine/lib/sdl/CMakeLists.txt
index 5bdf2f1497..8395bab26f 100644
--- a/Engine/lib/sdl/CMakeLists.txt
+++ b/Engine/lib/sdl/CMakeLists.txt
@@ -1,4 +1,4 @@
-if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
+if(${CMAKE_CURRENT_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
   message(FATAL_ERROR "Prevented in-tree built. Please create a build directory outside of the SDL source code and call cmake from there")
 endif()