diff --git a/src/evalwindow.c b/src/evalwindow.c
index 492269e..e00747a 100644
--- a/src/evalwindow.c
+++ b/src/evalwindow.c
@@ -673,6 +673,10 @@
     win_T	*save_curwin;
     tabpage_T	*save_curtab;
 
+    // Return an empty string if something fails.
+    rettv->v_type = VAR_STRING;
+    rettv->vval.v_string = NULL;
+
     if (wp != NULL && tp != NULL)
     {
 	pos_T	curpos = wp->w_cursor;