diff --git a/ansible_mitogen/services.py b/ansible_mitogen/services.py
index 058dac1c..7bc59135 100644
--- a/ansible_mitogen/services.py
+++ b/ansible_mitogen/services.py
@@ -128,17 +128,21 @@ class FileService(mitogen.service.Service):
             isinstance(args, tuple) and
             len(args) == 2 and
             args[0] in ('register', 'fetch') and
-            isinstance(args[1], str)
+            isinstance(args[1], basestring)
         )
 
     def dispatch(self, args, msg):
-        cmd, path = msg
+        cmd, path = args
         return getattr(self, cmd)(path, msg)
 
     def register(self, path, msg):
         if not mitogen.core.has_parent_authority(msg):
             raise mitogen.core.CallError(self.unprivileged_msg)
 
+        if path in self._paths:
+            return
+
+        LOG.info('%r: registering %r', self, path)
         with open(path, 'rb') as fp:
             self._paths[path] = zlib.compress(fp.read())