diff --git a/src/dbus_fast/message_bus.py b/src/dbus_fast/message_bus.py
index e54728d..7a8d733 100644
--- a/src/dbus_fast/message_bus.py
+++ b/src/dbus_fast/message_bus.py
@@ -878,7 +878,10 @@ class BaseMessageBus:
     ) -> None:
         """This is the callback that will be called when a method call is."""
         args = ServiceInterface._c_msg_body_to_args(msg) if msg.unix_fds else msg.body
-        result = method.fn(interface, *args)
+        kwargs = {}
+        if method.caller_argument is not None:
+            kwargs = {method.caller_argument: msg.sender}
+        result = method.fn(interface, *args, **kwargs)
         if send_reply is BLOCK_UNEXPECTED_REPLY or _expects_reply(msg) is False:
             return
         body_fds = ServiceInterface._c_fn_result_to_body(
diff --git a/src/dbus_fast/service.pxd b/src/dbus_fast/service.pxd
index f1903d6..a376f30 100644
--- a/src/dbus_fast/service.pxd
+++ b/src/dbus_fast/service.pxd
@@ -16,6 +16,7 @@ cdef class _Method:
     cdef public str out_signature
     cdef public SignatureTree in_signature_tree
     cdef public SignatureTree out_signature_tree
+    cdef public str caller_argument
 
 
 
diff --git a/src/dbus_fast/service.py b/src/dbus_fast/service.py
index 0b65b96..fbd829a 100644
--- a/src/dbus_fast/service.py
+++ b/src/dbus_fast/service.py
@@ -71,6 +71,7 @@ class _Method:
             for type_ in get_signature_tree(out_signature).types:
                 out_args.append(intr.Arg(type_, intr.ArgDirection.OUT))
 
+        self.caller_argument = caller_arg
         self.name = name
         self.fn = fn
         self.disabled = disabled
@@ -79,7 +80,6 @@ class _Method:
         self.out_signature = out_signature
         self.in_signature_tree = get_signature_tree(in_signature)
         self.out_signature_tree = get_signature_tree(out_signature)
-        self.caller_argument = caller_arg
 
 
 def method(
@@ -123,7 +123,7 @@ def method(
         raise TypeError("name must be a string")
     if type(disabled) is not bool:
         raise TypeError("disabled must be a bool")
-    if type(inject_caller) is not bool or type(caller_arg) is not str:
+    if type(inject_caller) is not bool and type(inject_caller) is not str:
         raise TypeError("inject_caller must be a string or bool")
 
     caller_arg = None
diff --git a/tests/service/test_methods.py b/tests/service/test_methods.py
index 9f7d719..ccbadab 100644
--- a/tests/service/test_methods.py
+++ b/tests/service/test_methods.py
@@ -60,6 +60,16 @@ class ExampleInterface(ServiceInterface):
         assert type(self) is ExampleInterface
         raise DBusError("test.error", "an error occurred")
 
+    @method(inject_caller=True)
+    def echo_caller(self, caller: str | None = None) -> "s":
+        assert type(self) is ExampleInterface
+        return caller
+
+    @method(inject_caller="source")
+    def echo_source(self, source: str | None = None) -> "s":
+        assert type(self) is ExampleInterface
+        return source
+
 
 class AsyncInterface(ServiceInterface):
     def __init__(self, name):
@@ -108,6 +118,16 @@ class AsyncInterface(ServiceInterface):
         assert type(self) is AsyncInterface
         raise DBusError("test.error", "an error occurred")
 
+    @method(inject_caller=True)
+    async def echo_caller(self, caller: str | None = None) -> "s":
+        assert type(self) is AsyncInterface
+        return caller
+
+    @method(inject_caller="source")
+    async def echo_source(self, source: str | None = None) -> "s":
+        assert type(self) is AsyncInterface
+        return source
+
 
 @pytest.mark.parametrize("interface_class", [ExampleInterface, AsyncInterface])
 @pytest.mark.asyncio
@@ -216,6 +236,14 @@ async def test_methods(interface_class):
         'test.interface.does_not_exist with signature "" could not be found'
     ]
 
+    reply = await call("echo_caller")
+    assert reply.message_type == MessageType.METHOD_RETURN, reply.body[0]
+    assert reply.body[0] == bus2.unique_name
+
+    reply = await call("echo_source")
+    assert reply.message_type == MessageType.METHOD_RETURN, reply.body[0]
+    assert reply.body[0] == bus2.unique_name
+
     bus1.disconnect()
     bus2.disconnect()
     bus1._sock.close()