Factual error: The movie takes place in 1850-51, and yet when the Rabbi is challenged to a shootout in San Francisco, the weapon he is handed is an 1858 Remington New Model Army revolver.

Factual error: The rabbi, Avram, shows his partner, Tommy, a photograph of his betrothed. However, in 1850-51, it would not have been on photographic paper, but either a tintype or a daguerreotype, on metal or glass.

Other: When Harrison Ford and Gene Wilder are being chased by the bad guys, they have to dismount and walk on Saturday because Gene is a Rabbi. However, close to sundown, the bad guys are getting close, so they're discussing whether the sun is setting, and there is a shot of the sun going behind a ridge. When the actors are shown again they are in full light, and not in shadow as they would be if the sun was going down, even though Gene is bobbing up and down as if he's making the sun go higher or lower by the position of his head. (This is so that they can remount once the sun has gone down, as the Jewish day of rest will have ended.)