functions-framework does not use the sourced venv

I am using the functions-framework to develop on my local machine and I have created a python venv for the project. Following is a description of my issue:
- I have installed the firebase_admin lib within the venv and I am importing it within the src code.
- I am running the command: `functions-framework --source ./src/main.py --target main`
- The above command fails with following error: `ModuleNotFoundError: No module named 'firebase_admin'`
- The above error **does not** occur if I install the firebase_admin lib outside the venv (global scopte)

Is there a way to specify which python env to use or is always set to the global python scope?