Reset the flag that indicates option {name} was set. Thus it looks like it still has the default value. Use like this: set ambiwidth=double call test_option_not_set('ambiwidth') Now the 'ambiwidth' option behaves like it was never changed, even though the value is "double". Only to be used for testing! Can also be used as a |method|: GetOptionName()->test_option_not_set()