Many eclectic Brooklyn coffee shops serve hot coffee in only one size. Maybe that explains the trouble Sen. Charles Schumer had with his order Wednesday morning.

The New York Democrat was spotted having a mild disagreement with a barista at the Cups and Co. coffee shop in the Russell Senate Office Building about the size of his brew.

Schumer went in to buy his own coffee, but after spotting a young staffer in the line, he offered to treat her to one as well. She asked him for a large coffee. Schumer elected to score himself a venti.

His mind made up, Schumer ordered one large and one venti from a perplexed barista.

After an exasperating exchange that lasted at least a couple of minutes, Schumer realized he really wanted two venti beverages, pointing out that the menu board used the Italian names for drink sizes.

The staffer seemed to signal in response that — like many Cups regulars — the baristas already knew her order.

At least Schumer didn’t try to order a venti from Dunkin’ Donuts.