@@ -772,6 +772,9 @@ func (f *FlagSet) parseOne() (bool, string, error) {

 			f.usage()

 			return false, "", ErrHelp

 		}

+		if len(name) > 0 && name[0] == '-' {

+			return false, "", f.failf("flag provided but not defined: -%s", name)

+		}

 		return false, name, ErrRetry

 	}

 	if fv, ok := flag.Value.(boolFlag); ok && fv.IsBoolFlag() { // special case: doesn't need an arg