(Sorry for the delay in responding -- I thought I had written a reply, but apparently I haven't figured out the interface software, entirely, yet). Anyway, I've decided to rewrite the offending code. It appears as if the actual problem was something inside the block guarded by if ( defined $factories{ $tmpf}) -- cleaning that error up removed the warning. I'll try to post a more complete code snippet next time - I had intended to clean it up so it would be least confusing, and clearly went too far. Thanks to all who replied. I was rather surprised at the quantity (and helpfulness) of the responses.