Users (erroneously) type a short URL in the Google search box instead of the address bar. How to make it navigate instead of showing search results?

I’m using a URL shortener to publish pronounceable URLs for my pages so I can tell people something like, "Visit mydomain.com/slug to solve that problem." If people go to the address bar of their browser and enter mydomain.com/slug URL there, then the shortened URL works, and it redirects them to the intended destination page. But if a non-technical user goes to the Google search page and enters mydomain.com/slug into the search box there, apparently, Google apparently isn’t smart enough to recognize that they typed in a URL. It tries instead to search for the URL as keywords and comes back with a list of search results.

When I click "New Tab" in my browser, I know the difference between the address bar and the search box, but many non-technical users don’t, and Google gives the same instructions in both places. Both locations claim to accept both search terms and URLs, but apparently they have different logic for determining which is which. For them to behave differently and not follow the URL when it’s typed into the search box instead of the browser address bar seems to be a fatal flaw in the entire concept of shortened URLs – unless there’s something else I can do to make them work regardless of which field someone types them into. Certainly I can’t be the only one facing this.

What can I do to teach Google that my shortened URL is indeed a URL and when someone types it in the search box, it should go to the place where that URL redirects to?