diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 489b23da2a..2adbdb8635 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -86,6 +86,7 @@ if(APPLE)
     set(LIBRARY_SOURCE_FILES
         ${LIBRARY_SOURCE_FILES}
         get_focused_window_mac.cc
+        lib/osx/Kopsik/MacOSVersionChecker.mm
     )
     set(ADDITIONAL_LIBRARIES
         "-framework Foundation"