diff --git a/form.c b/form.c
index da115fa..805505f 100644
--- a/form.c
+++ b/form.c
@@ -481,7 +481,7 @@ formUpdateBuffer(Anchor *a, Buffer *buf, FormItemList *form)
 		spos = a->start.pos;
 		epos = a->end.pos;
 	    }
-	    if (a->start.line != a->end.line || spos > epos)
+	    if (a->start.line != a->end.line || spos > epos || epos > l->len)
 		epos = spos;
 	    pos = form_update_line(l, &p, spos, epos, COLPOS(l, epos) - col,
 				   rows > 1,