Robot framework resource file not found

I want to use a resource file with the name clean_environment.robot on windows. It is in the same folder like my robot file (C:\Users\xxxxx\Desktop\git\src), which is callig the resource file.

Basic file 30.robot:

** Settings **
Resource    clean_environment.robot

** Test Cases **
MyTestCase
    Clean environment

I get the error:

[ ERROR ] Error in file
'C:\Users\xxxxx\Desktop\git\src\30.robot': 
Resource file 'Clean environment' does not exist.