How does one handle changes made to an api they depend one?

Hello,

I wanted to keep the title short however it lacks some context. My question is targeted towards Web APIs. Let's say I want to build a product that will use the Google map API. If one day Google modifies the API without telling anybody, how can I handle this change so the service is still usable for my customers and behaves as expected?

Ps: Sorry for the typo in the title