diff --git a/oasst-shared/oasst_shared/api_client.py b/oasst-shared/oasst_shared/api_client.py
index e8439517..404521db 100644
--- a/oasst-shared/oasst_shared/api_client.py
+++ b/oasst-shared/oasst_shared/api_client.py
@@ -70,7 +70,7 @@ class OasstApiClient:
         if response.status >= 300:
             data = await response.json()
             try:
-                oasst_error = protocol_schema.OasstErrorResponse(**data)
+                oasst_error = protocol_schema.OasstErrorResponse(**(data or {}))
                 raise OasstError(
                     error_code=oasst_error.error_code,
                     message=oasst_error.message,
diff --git a/oasst-shared/tests/test_oasst_api_client.py b/oasst-shared/tests/test_oasst_api_client.py
index 8649d891..fdb743ce 100644
--- a/oasst-shared/tests/test_oasst_api_client.py
+++ b/oasst-shared/tests/test_oasst_api_client.py
@@ -106,3 +106,23 @@ async def test_can_handle_oasst_error_from_api(
 
     with pytest.raises(OasstError):
         await oasst_api_client_fake_http.post("/some-path", data={})
+
+
+@pytest.mark.asyncio
+async def test_can_handle_unknown_error_from_api(
+    oasst_api_client_fake_http: OasstApiClient,
+    mock_http_session: MockClientSession,
+):
+    response_body = "Internal Server Error"
+    status_code = 500
+
+    mock_http_session.set_response(
+        mock.AsyncMock(
+            status=status_code,
+            text=mock.AsyncMock(return_value=response_body),
+            json=mock.AsyncMock(return_value=None),
+        )
+    )
+
+    with pytest.raises(OasstError):
+        await oasst_api_client_fake_http.post("/some-path", data={})