Character mistake: When the alarms go off in the police station indicating the code 187 all the police officers are confused as to what is going on since they know nothing of MDKs. Zack Lamb should have already known what the code meant, yet he never says anything and just waits for everyone to figure it out.
Character mistake: In the scene where John Spartan goes into the sewers, he has a conversation with a Spanish-speaking woman. At the end of their conversation the woman says "Gracias" (correct Spanish) to which Spartan replies "Prego", which is Italian. Up until that point Spartan spoke perfect Spanish. (01:23:30)