diff --git a/src/kits/interface/interface.src b/src/kits/interface/interface.src
index bfa55d5254..ea745a71db 100644
--- a/src/kits/interface/interface.src
+++ b/src/kits/interface/interface.src
@@ -34,4 +34,5 @@ INTERFACE_KIT_SOURCE =
 	TextGapBuffer.cpp
 	TextView.cpp
 	UndoBuffer.cpp
+	WidthBuffer.cpp
 ;