diff --git a/g10/build-packet.c b/g10/build-packet.c
index 14e40a1bf..266bf54e4 100644
--- a/g10/build-packet.c
+++ b/g10/build-packet.c
@@ -1504,9 +1504,12 @@ do_signature( IOBUF out, int ctb, PKT_signature *sig )
     {
       iobuf_put( a, 3 );
 
-      /* Version 3 packets don't support subpackets.  */
-      log_assert (! sig->hashed);
-      log_assert (! sig->unhashed);
+      /* Version 3 packets don't support subpackets.  Actually we
+       * should never get to here but real life is different and thus
+       * we now use a log_fatal instead of a log_assert here. */
+      if (sig->hashed || sig->unhashed)
+        log_fatal ("trying to write a subpacket to a v3 signature (%d,%d)\n",
+                   !!sig->hashed, !!sig->unhashed);
     }
   else
     iobuf_put( a, sig->version );