diff --git a/ssh.c b/ssh.c
index 0edaf932..acc4598b 100644
--- a/ssh.c
+++ b/ssh.c
@@ -884,6 +884,15 @@ static int ssh2_rdpkt(unsigned char **data, int *datalen)
     st->len = GET_32BIT(pktin.data);
     st->pad = pktin.data[4];
 
+    /*
+     * _Completely_ silly lengths should be stomped on before they
+     * do us any more damage.
+     */
+    if (st->len < 0 || st->pad < 0 || st->len + st->pad < 0) {
+	bombout(("Incoming packet was garbled on decryption"));
+	crReturn(0);
+    }
+
     /*
      * This enables us to deduce the payload length.
      */