diff --git a/moduli.c b/moduli.c
index 17c7281..371319d 100644
--- a/moduli.c
+++ b/moduli.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: moduli.c,v 1.3 2003/12/07 06:34:18 djm Exp $ */
+/* $OpenBSD: moduli.c,v 1.4 2003/12/09 13:52:55 dtucker Exp $ */
 /*
  * Copyright 1994 Phil Karn <karn@qualcomm.com>
  * Copyright 1996-1998, 2003 William Allen Simpson <wsimpson@greendragon.com>
@@ -550,6 +550,15 @@
 			continue;
 		}
 
+		/*
+		 * Primes with no known generator are useless for DH, so
+		 * skip those.
+		 */
+		if (generator_known == 0) {
+			debug2("%10u: no known generator", count_in);
+			continue;
+		}
+
 		count_possible++;
 
 		/*