diff --git a/src/dispatch/function.py b/src/dispatch/function.py
index 798af504..c996ff20 100644
--- a/src/dispatch/function.py
+++ b/src/dispatch/function.py
@@ -59,6 +59,7 @@ def __init__(
         name: str,
         primitive_func: PrimitiveFunctionType,
         func: Callable,
+        coroutine: bool = False,
     ):
         self._endpoint = endpoint
         self._client = client
@@ -66,10 +67,7 @@ def __init__(
         self._primitive_func = primitive_func
         # FIXME: is there a way to decorate the function at the definition
         #  without making it a class method?
-        if inspect.iscoroutinefunction(func):
-            self._func = durable(self._call_async)
-        else:
-            self._func = func
+        self._func = durable(self._call_async) if coroutine else func
 
     def __call__(self, *args, **kwargs):
         return self._func(*args, **kwargs)
@@ -204,7 +202,7 @@ def primitive_func(input: Input) -> Output:
         primitive_func.__qualname__ = f"{func.__qualname__}_primitive"
         primitive_func = durable(primitive_func)
 
-        return self._register(func, primitive_func)
+        return self._register(primitive_func, func, coroutine=False)
 
     def _register_coroutine(self, func: Callable) -> Function:
         logger.info("registering coroutine: %s", func.__qualname__)
@@ -218,14 +216,14 @@ def primitive_func(input: Input) -> Output:
         primitive_func.__qualname__ = f"{func.__qualname__}_primitive"
         primitive_func = durable(primitive_func)
 
-        return self._register(func, primitive_func)
+        return self._register(primitive_func, func, coroutine=True)
 
     def _register_primitive_function(self, func: PrimitiveFunctionType) -> Function:
         logger.info("registering primitive function: %s", func.__qualname__)
-        return self._register(func, func)
+        return self._register(func, func, coroutine=inspect.iscoroutinefunction(func))
 
     def _register(
-        self, func: Callable, primitive_func: PrimitiveFunctionType
+        self, primitive_func: PrimitiveFunctionType, func: Callable, coroutine: bool
     ) -> Function:
         name = func.__qualname__
         if name in self._functions:
@@ -233,7 +231,7 @@ def _register(
                 f"function or coroutine already registered with name '{name}'"
             )
         wrapped_func = Function(
-            self._endpoint, self._client, name, primitive_func, func
+            self._endpoint, self._client, name, primitive_func, func, coroutine
         )
         self._functions[name] = wrapped_func
         return wrapped_func