diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8d079f074c7..1435859851a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -241,7 +241,7 @@ include(CPack)
 # sure that we don't have any stray generated files lying around in the tree
 # (which would end up getting picked up by header search, instead of the correct
 # versions).
-if( CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT MSVC_IDE )
+if( CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_CURRENT_BINARY_DIR AND NOT MSVC_IDE )
   message(FATAL_ERROR "In-source builds are not allowed.
 CMake would overwrite the makefiles distributed with LLVM.
 Please create a directory and run cmake from there, passing the path