diff --git a/src/Makefile.am b/src/Makefile.am
index ab93038cc3..3624d2a11c 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -214,6 +214,8 @@ lyx_SOURCES = \
 	undo.h \
 	undo_funcs.C \
 	undo_funcs.h \
+	undostack.C \
+	undostack.h \
 	vc-backend.C \
 	vc-backend.h \
 	version.C \