There are several synonyms for the phrase "liable to mistake." One common synonym is "prone to error," which implies a tendency or likelihood to make mistakes. Another option is "fallible," which suggests a susceptibility to error or imperfection. "Erroneous" can also be used as a synonym, indicating a mistake or inaccuracy. "Imperfect" or "flawed" can be used to describe a person's work or performance, while "imprecise" or "inexact" may refer to the accuracy of a statement or measurement. Ultimately, there are many ways to describe someone or something that is prone to making mistakes, depending on the context and intended meaning.