Fix for issue #924
Fix for issue #924

As mentioned in https://github.com/coreos/prometheus-operator/issues/924#issuecomment-362859346 .
coreos/prometheus-operator,brancz/prometheus-operator,jescarri/prometheus-operator,gianrubio/prometheus-operator,jescarri/prometheus-operator,coreos/prometheus-operator,brancz/prometheus-operator,gianrubio/prometheus-operator,brancz/prometheus-operator,gianrubio/prometheus-operator