diff --git a/flow/project.py b/flow/project.py
index 2cd448e4f..a5646794d 100644
--- a/flow/project.py
+++ b/flow/project.py
@@ -697,7 +697,7 @@ def __call__(self, func=None, /, *, directives=None):
             return functools.partial(self._internal_call, directives=directives)
         return self._internal_call(func, directives=directives)
 
-    def _internal_call(self, func, *, directives):
+    def _internal_call(self, func, /, *, directives):
         if not any(
             func == op_func for _, op_func in self._project._OPERATION_FUNCTIONS
         ):