Ben McKenzie Ben McKenzie

"Holy concrete wall, Batman!"

That was actor Ben McKenzie's good-natured response after he sustained a nasty gash on his head while filming Gotham.

McKenzie, who plays young Det. Gordon in Fox's upcoming Batman origin story, was injured on the show's set Friday (his birthday) while he was shooting a fight sequence.

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The actor posted three photos on Instagram — one of which showed his head bleeding and the other with him giving a thumbs-up while appearing to get stitches.

"Happy Birthday to me," McKenzie captioned one. "Fight sequence gone awry. Don't ram your head into concrete pillars kids. #gotham."

McKenzie says he'll be back to work on Monday.

On the Set: Gotham's stunt coordinator teaches us how to fake a fight: