--- a/lib/Quancom/Result.pm	Tue Jan 06 15:07:03 2009 +0100
+++ b/lib/Quancom/Result.pm	Tue Jan 06 22:33:39 2009 +0100
@@ -59,11 +59,13 @@
 
 sub error_message {
     my $self = shift;
+    my $e = @_ ? shift : $self->{error_code};
 
     return undef if !@_ and $self->{ok};
 
+    return "unknown error" if not defined $e or $e > 3;
     return +("checksum error", "character error", "invalid command",
-        "invalid width")[ defined $_[0] ? $_[0] : $self->{error_code} ];
+        "invalid width")[$e];
 }
 
 1;