Can’t read multiple custom fields

I am a bit at a loss.

I have a custom field with key (let’s say) ‘foo’ defined, and in one post this is used twice, once with ‘bar’, once with ‘fraggle’ as values.

There is no problem calling ‘bar’ with get_post_meta($post_id, 'foo', TRUE), so obviously the fields are there, and in the right post.

However, when I try to call both of them into an array as in

if(get_post_custom_values('foo')) {
/* do something */
foreach (get_post_custom_values('foo') as $single_foo) { /* do some more and so on

I never even get to do something, let alone some more. Am I missing something important here, am I blindfolded?