(CNN) -- Watching the movie "Lincoln" on Saturday, Rep. Joe Courtney was perplexed during the climactic scene.
Two of his predecessors from nearly 150 years ago, lawmakers representing the state of Connecticut in 1865, are seen voting against the constitutional amendment to end slavery.
Courtney asked the Congressional Research Service for the records, and sure enough, all four representatives from Connecticut voted yes on the 13th amendment.
But in the film, we see the fictional lawmakers Augustus Benjamin and Arthur Bentleigh of Connecticut each vote "Nay."
"I could not believe my own eyes and ears," Courtney said. In a letter of protest to director Steven Spielberg, he said that although he thinks overall the film is tremendous and compelling, "placing the State of Connecticut on the wrong side of the historic and divisive fight over slavery is a distortion of easily verifiable facts."
Screenwriter Tony Kushner conceded the discrepancy but defended the film.
"None of the key moments of that story -- the overarching story our film tells -- are altered," he said in a statement Thursday. He explained that the alterations were made to serve the narrative that the outcome of the vote was in doubt until the very end.
"I hope nobody is shocked to learn that I also made up dialogue and imagined encounters and invented characters," he added.
"I'm sorry if anyone in Connecticut felt insulted by these 15 seconds of the movie," Kushner said, but "this is a dramatic film and not an attack on their home state."
Still, Courtney said Friday that he hoped the movie would be changed before it is released on DVD on February 26.
"The four members of Connecticut's delegation ... deserved a better legacy than the screenplay portrayed," he said.
Historian Christian McWhirter, a researcher with the Papers of Abraham Lincoln, supported the congressman's objection.
"It seems like such an unnecessary error," he said. Nevertheless, he added, "it shouldn't overshadow the fact that overall, this is a very strong and accurate portrayal of what actually happened."
Going through the movie script vote by vote, CNN found that the important details are correct. By the narrowest of margins, after a breathless and unpredictable roll call, the amendment passes, with most Republicans in favor but many Democrats opposed.
Six of the lawmakers in the film actually existed and cast real votes, while the rest are apparently fictitious. No other vote discrepancies were found in the scene.
Columbia University historian Eric Foner said the voting in the film is not the only discrepancy, but for dramatic effect, some poetic license is fine in such a movie.
"It is historical fiction -- a noble genre going back to Shakespeare and well before -- not history," he said.
Indeed, the movie makes no claims to be a documentary, but is rather a historical film.
In the style of a political thriller, it depicts President Lincoln's efforts to get a ban on slavery passed in Washington, using a combination of persuasion, inspiration, horse-trading and arm-twisting. The film has been nominated for 12 Academy Awards and has been a success both with the critics and at the box office.
Disney, the distributor, and representatives for Spielberg did not reply to inquiries from CNN on Wednesday.
McWhirter defended the movie.
" 'Lincoln' is an exceptionally good Hollywood historical film," he said, "so I think we have to have a certain amount of tolerance for a certain amount of error."
CNN's JD Cargill contributed to this report.