WASHINGTON—When Neil Armstrong first spoke from the moon, he said one thing and people on Earth heard another.

What the world heard was grammatically flubbed: “That’s one small step for man; one giant leap for mankind.”

Armstrong insists he said: “That’s one small step for ‘a’ man.” It’s just that people just didn’t hear it.

Science, and the National Aeronautics and Space Administration (NASA), back up Armstrong.

“The ‘a’ was intended,” Armstrong said in a rare press conference in 1999. “I thought I said it. I can’t hear it when I listen on the radio reception here on Earth, so I’ll be happy if you just put it in parentheses.”

But in 2006, a computer analysis found evidence that Armstrong said what he said he had said.

Peter Shann Ford, an Australian computer programmer, ran a software analysis looking at sound waves and found a wave that would have been the missing “a.” It lasted 35 milliseconds, much too quick to be heard.

Armstrong and experts at the Smithsonian Institution looked at the evidence and it was convincing, according to Smithsonian space curator Roger Launius.

“I find the technology interesting and useful,” Armstrong said in a statement. “I also find his conclusion persuasive.”

And NASA stands by its moon man.

“If Neil Armstrong says there was an ‘a,’ then as far as we’re concerned, there was ‘a,’” said NASA spokesperson Michael Cabbage.

Armstrong is famously a man of few words, but he and NASA insist that he came up with those famous and profound words on his own. Launius believes him.

In a 2001 NASA oral history, Armstrong said: “I thought about it after landing, and because we had a lot of other things to do, it was not something that I really concentrated on, but just something that was kind of passing around subliminally or in the background. But it, you know, was a pretty simple statement, talking about stepping off something. Why, it wasn’t a very complex thing. It was what it was.”