diff --git a/build/bakefiles/files.bkl b/build/bakefiles/files.bkl
index 35f105b72a..f67c8c441e 100644
--- a/build/bakefiles/files.bkl
+++ b/build/bakefiles/files.bkl
@@ -1690,7 +1690,7 @@ IMPORTANT: please read docs/tech/tn0016.txt before modifying this file!
     src/cocoa/main.cpp
     src/cocoa/menu.mm
     src/cocoa/menuitem.mm
-    src/cocoa/pen.cpp
+    src/cocoa/pen.mm
     src/cocoa/radiobox.mm
     src/cocoa/radiobut.mm
     src/cocoa/region.cpp