diff --git a/src/werror.c b/src/werror.c
index 1c101fd398ae144afcd29a6f16f661083e3e4536..08b1dbd7a295348c5c42392a28c075ebbfadf2d7 100644
--- a/src/werror.c
+++ b/src/werror.c
@@ -404,9 +404,11 @@ werror_vformat(const char *f, va_list args)
 	      {
 		int atom = va_arg(args, int);
 		
-		assert(atom);
-
-		werror_write(get_atom_length(atom), get_atom_name(atom));
+                if (atom)
+                  werror_write(get_atom_length(atom), get_atom_name(atom));
+		else
+                  werror_write(9, "<unknown>");
+		break;
 		
 		break;
 	      }