Getting error "_git:19: command not found: _default" when implementing git-completion scripts in zsh

Question

I am trying to configure my zsh terminal to use git's tab completion script.

Some of my trouble may be coming from a non-standard file structure:

$ tree ~/Scripts
/Users/luigi/Scripts
├── connect.sh
├── git-completion.sh
├── git-completion.zsh
├── git-prompt.sh
└── pshell_connect.sh

My zshrc config details for tab completion:

fpath=(~/Scripts $fpath)
source ~/Scripts/git-prompt.sh
zstyle ':completion:*:*:git:*' script ~/Scripts/git-completion.sh
source ~/Scripts/git-completion.zsh

And again the error message when I start a session:

_git:19: command not found: _default

Am I maybe missing some additional dependencies or did I just goof up something on the configuration? I'm coming from Linux so it's probably the latter.

I have tried reading the source and I see the _git () function. I am assuming the error originates from this line:

let _ret && _default && _ret=0

where the _default () function is being evaluated, but I have no idea where this is supposed to be defined.