diff --git a/dropbox/dropbox_client.py b/dropbox/dropbox_client.py
index 358f062..b5f0efe 100644
--- a/dropbox/dropbox_client.py
+++ b/dropbox/dropbox_client.py
@@ -18,6 +18,7 @@
 from stone.backends.python_rsrc import stone_serializers
 
 from dropbox import files
+from dropbox.auth import AuthError as AuthErrorUnion
 from dropbox.auth import (
     AuthError_validator,
     RateLimitError_validator,
@@ -726,8 +727,19 @@ def raise_dropbox_error_for_resp(self, res):
                 "Expected content-type to be application/json, got %r"
                 % res.headers.get("content-type")
             )
-            err = stone_serializers.json_compat_obj_decode(AuthError_validator, res.json()["error"])
-            raise AuthError(request_id, err)
+            raw_error = res.json()["error"]
+            # Stone reserves the catch-all tag for unknown variants and rejects
+            # it on the wire, even with strict=False. Some 401 responses send
+            # "other" explicitly; keep those as authentication errors too.
+            if raw_error == "other" or (
+                isinstance(raw_error, dict) and raw_error.get(".tag") == "other"
+            ):
+                err = AuthErrorUnion.other
+            else:
+                err = stone_serializers.json_compat_obj_decode(
+                    AuthError_validator, raw_error, strict=False
+                )
+            raise AuthError(request_id, err, body=res.text)
         elif res.status_code == HTTP_STATUS_INVALID_PATH_ROOT:
             err = stone_serializers.json_compat_obj_decode(
                 PathRootError_validator, res.json()["error"]
diff --git a/dropbox/exceptions.py b/dropbox/exceptions.py
index 389c1cc..409294f 100644
--- a/dropbox/exceptions.py
+++ b/dropbox/exceptions.py
@@ -68,10 +68,13 @@ def __repr__(self):
 
 
 class AuthError(HttpError):
-    """Errors due to invalid authentication credentials."""
+    """Errors due to invalid authentication credentials.
 
-    def __init__(self, request_id, error):
-        super(AuthError, self).__init__(request_id, 401, None)
+    The optional ``body`` contains the original HTTP response body, when available.
+    """
+
+    def __init__(self, request_id, error, body=None):
+        super(AuthError, self).__init__(request_id, 401, body)
         self.error = error
 
     def __repr__(self):
diff --git a/test/unit/test_dropbox_unit.py b/test/unit/test_dropbox_unit.py
index 1f49420..2a3c54c 100644
--- a/test/unit/test_dropbox_unit.py
+++ b/test/unit/test_dropbox_unit.py
@@ -788,6 +788,51 @@ def test_refresh_raises_after_exhausting_retries(self, server_error_session_inst
         # Initial attempt + 2 retries.
         assert server_error_session_instance.post.call_count == 3
 
+    @pytest.mark.parametrize(
+        "raw_error, expected_tag",
+        [
+            ("other", "other"),
+            ({".tag": "other"}, "other"),
+            ("future_auth_error", "other"),
+            ({".tag": "future_auth_error", "details": "new server error"}, "other"),
+            ("invalid_access_token", "invalid_access_token"),
+            ({".tag": "invalid_access_token", "future_field": True}, "invalid_access_token"),
+            (
+                {
+                    ".tag": "missing_scope",
+                    "required_scope": "files.content.write",
+                    "future_field": True,
+                },
+                "missing_scope",
+            ),
+        ],
+    )
+    def test_upload_preserves_auth_errors(self, session_instance, mocker, raw_error, expected_tag):
+        response = requests.Response()
+        response.status_code = 401
+        response.headers = {
+            "content-type": "application/json",
+            "x-dropbox-request-id": "auth-request-id",
+        }
+        response._content = json.dumps(
+            {"error": raw_error, "error_summary": "authentication failed"}
+        ).encode("utf-8")
+        session_instance.post.return_value = response
+        dbx = Dropbox(ACCESS_TOKEN, session=session_instance)
+        refresh = mocker.patch.object(dbx, "refresh_access_token")
+
+        with pytest.raises(AuthError) as caught:
+            dbx.files_upload(b"contents", "/test.txt")
+
+        assert getattr(caught.value.error, "is_" + expected_tag)()
+        if expected_tag == "missing_scope":
+            assert caught.value.error.get_missing_scope().required_scope == "files.content.write"
+        assert caught.value.status_code == 401
+        assert caught.value.request_id == "auth-request-id"
+        assert caught.value.body == response.text
+        session_instance.post.assert_called_once()
+        refresh.assert_not_called()
+
     def test_refresh_on_expired_access_token_uses_client_scope(self, session_instance, mocker):
         # A 401 expired_access_token triggers a refresh, which must request the
         # scope the client was configured with, like check_and_refresh_access_token.