Erlang is a functional, concurrent, high-level general-purpose programming language, running on the BEAM virtual machine, which is dynamically typed. Similarly to Python, type annotations are supported in the syntax, but not checked at compilation or runtime. However, there are some tools which aim to provide type checking support for Erlang, the Gradualizer type checker being one of the most promising. While Gradualizer provides clear type error messages in most cases, the messages become unspecific and lack a specific location when polymorphic functions are involved. The goal of this thesis is to implement the Local type application synthesis for Gradualizer and thus improve the error messages related to polymorphic function applications.