1 files changed, 2 insertions, 0 deletions
diff --git a/lib.c b/lib.c
index ba6ebd4..8078db0 100644
--- a/lib.c
+++ b/lib.c
@@ -390,6 +390,8 @@ void newfld(int n)	/* add field n after end of existing lastfld */
 
 void setlastfld(int n)	/* set lastfld cleaning fldtab cells if necessary */
 {
+	if (n < 0)
+		FATAL("cannot set NF to a negative value");
 	if (n > nfields)
 		growfldtab(n);