diff --git a/docs/ba_module.md b/docs/ba_module.md
index d03b39be..eafe7be5 100644
--- a/docs/ba_module.md
+++ b/docs/ba_module.md
@@ -1,5 +1,5 @@
 <!-- THIS FILE IS AUTO GENERATED; DO NOT EDIT BY HAND -->
-<h4><em>last updated on 2021-09-08 for Ballistica version 1.6.5 build 20391</em></h4>
+<h4><em>last updated on 2021-09-09 for Ballistica version 1.6.5 build 20391</em></h4>
 <p>This page documents the Python classes and functions in the 'ba' module,
  which are the ones most relevant to modding in Ballistica. If you come across something you feel should be included here or could be better explained, please <a href="mailto:support@froemling.net">let me know</a>. Happy modding!</p>
 <hr>
diff --git a/tools/efro/message.py b/tools/efro/message.py
index 3f9439a6..fa063e99 100644
--- a/tools/efro/message.py
+++ b/tools/efro/message.py
@@ -56,7 +56,11 @@ class Response:
 @ioprepped
 @dataclass
 class RemoteErrorResponse(Response):
-    """Message saying some error has occurred on the other end."""
+    """Message saying some error has occurred on the other end.
+
+    This type is unique in that it is not returned to the user; it
+    instead results in a local exception being raised.
+    """
     error_message: Annotated[str, IOAttrs('m')]
     error_type: Annotated[RemoteErrorType, IOAttrs('t')]
 
@@ -122,6 +126,13 @@ class MessageProtocol:
             self.response_types_by_id[r_id] = r_type
             self.response_ids_by_type[r_type] = r_id
 
+        # If they didn't register RemoteErrorResponse, do so with a special
+        # -1 id which ensures it will never conflict with user messages.
+        if RemoteErrorResponse not in self.response_ids_by_type:
+            assert self.response_types_by_id.get(-1) is None
+            self.response_types_by_id[-1] = RemoteErrorResponse
+            self.response_ids_by_type[RemoteErrorResponse] = -1
+
         # Some extra-thorough validation in debug mode.
         if __debug__:
             # Make sure all Message types' return types are valid
@@ -155,32 +166,22 @@ class MessageProtocol:
         self.log_remote_exceptions = log_remote_exceptions
         self.trusted_client = trusted_client
 
-    def encode_message(self,
-                       message: Message,
-                       is_error: bool = False) -> bytes:
+    def encode_message(self, message: Message) -> bytes:
         """Encode a message to bytes for transport."""
-        return self._encode(message, is_error, self.message_ids_by_type,
-                            'message')
+        return self._encode(message, self.message_ids_by_type, 'message')
 
-    def encode_response(self,
-                        response: Response,
-                        is_error: bool = False) -> bytes:
+    def encode_response(self, response: Response) -> bytes:
         """Encode a response to bytes for transport."""
-        return self._encode(response, is_error, self.response_ids_by_type,
-                            'response')
+        return self._encode(response, self.response_ids_by_type, 'response')
 
-    def _encode(self, message: Any, is_error: bool,
-                ids_by_type: Dict[Type, int], opname: str) -> bytes:
+    def _encode(self, message: Any, ids_by_type: Dict[Type, int],
+                opname: str) -> bytes:
         """Encode a message to bytes for transport."""
 
-        m_id: Optional[int]
-        if is_error:
-            m_id = -1
-        else:
-            m_id = ids_by_type.get(type(message))
-            if m_id is None:
-                raise TypeError(f'{opname} type is not registered in protocol:'
-                                f' {type(message)}')
+        m_id: Optional[int] = ids_by_type.get(type(message))
+        if m_id is None:
+            raise TypeError(f'{opname} type is not registered in protocol:'
+                            f' {type(message)}')
         msgdict = dataclass_to_dict(message)
 
         # Encode type as part of the message/response dict if desired
@@ -223,20 +224,22 @@ class MessageProtocol:
         assert isinstance(m_id, int)
         assert isinstance(msgdict, dict)
 
-        # Special case: a remote error occurred. Raise a local Exception.
-        if m_id == -1:
-            assert opname == 'response'
-            err = dataclass_from_dict(RemoteErrorResponse, msgdict)
-            if (self.preserve_clean_errors
-                    and err.error_type is RemoteErrorType.CLEAN):
-                raise CleanError(err.error_message)
-            raise RemoteError(err.error_message)
-
         # Decode this particular type.
         msgtype = types_by_id.get(m_id)
         if msgtype is None:
             raise TypeError(f'Got unregistered {opname} type id of {m_id}.')
-        return dataclass_from_dict(msgtype, msgdict)
+        out = dataclass_from_dict(msgtype, msgdict)
+
+        # Special case: a remote error occurred. Raise a local Exception
+        # instead of returning the message.
+        if isinstance(out, RemoteErrorResponse):
+            assert opname == 'response'
+            if (self.preserve_clean_errors
+                    and out.error_type is RemoteErrorType.CLEAN):
+                raise CleanError(out.error_message)
+            raise RemoteError(out.error_message)
+
+        return out
 
     def _get_module_header(self, part: str) -> str:
         """Return common parts of generated modules."""
@@ -640,7 +643,7 @@ class MessageReceiver:
                                    if self._protocol.trusted_client else
                                    'An unknown error has occurred.'),
                     error_type=RemoteErrorType.OTHER)
-            return self._protocol.encode_response(err_response, is_error=True)
+            return self._protocol.encode_response(err_response)
 
     async def handle_raw_message_async(self, msg: bytes) -> bytes:
         """Should be called when the receiver gets a message.