diff --git a/src/proto/undo.pro b/src/proto/undo.pro
index 8ac2323..5114ed0 100644
--- a/src/proto/undo.pro
+++ b/src/proto/undo.pro
@@ -7,6 +7,7 @@
 void u_undo __ARGS((int count));
 void u_redo __ARGS((int count));
 void u_sync __ARGS((void));
+void ex_undojoin __ARGS((exarg_T *eap));
 void u_unchanged __ARGS((buf_T *buf));
 void u_clearall __ARGS((buf_T *buf));
 void u_saveline __ARGS((linenr_T lnum));