diff --git a/src/kits/interface/interface.src b/src/kits/interface/interface.src
index 95bf28b20c..70f1f47dca 100644
--- a/src/kits/interface/interface.src
+++ b/src/kits/interface/interface.src
@@ -33,4 +33,5 @@ INTERFACE_KIT_SOURCE =
 	StyleBuffer.cpp
 	TextGapBuffer.cpp
 	TextView.cpp
+	UndoBuffer.cpp
 ;