diff --git a/modapp/transports/web_aiohttp.py b/modapp/transports/web_aiohttp.py
index ad5eb21..3b50460 100644
--- a/modapp/transports/web_aiohttp.py
+++ b/modapp/transports/web_aiohttp.py
@@ -43,19 +43,43 @@ def _get_cors_headers(cors_allow: str | None) -> dict[str, str]:
     return headers
 
 
-def _exception_to_response(error: Exception, converter: BaseConverter, cors_allow: str | None) -> Exception:
+def _exception_to_response(
+    error: Exception, converter: BaseConverter, cors_allow: str | None
+) -> Exception:
     if isinstance(error, NotFoundError):
-        return web.HTTPNotFound(headers=_get_cors_headers(cors_allow), body=converter.error_to_raw(error))
+        return web.HTTPNotFound(
+            headers=_get_cors_headers(cors_allow),
+            body=converter.error_to_raw(error),
+            content_type=_get_content_type(converter),
+        )
     elif isinstance(error, InvalidArgumentError):
-        return web.HTTPUnprocessableEntity(headers=_get_cors_headers(cors_allow), body=converter.error_to_raw(error))
+        return web.HTTPUnprocessableEntity(
+            headers=_get_cors_headers(cors_allow),
+            body=converter.error_to_raw(error),
+            content_type=_get_content_type(converter),
+        )
     elif isinstance(error, ServerError):
         # does the same as return statement below, but shows explicitly mapping of ServerError to
         # http error
-        return web.HTTPInternalServerError(headers=_get_cors_headers(cors_allow), body=converter.error_to_raw(error))
+        return web.HTTPInternalServerError(
+            headers=_get_cors_headers(cors_allow),
+            body=converter.error_to_raw(error),
+            content_type=_get_content_type(converter),
+        )
 
     return web.HTTPInternalServerError(headers=_get_cors_headers(cors_allow))
 
 
+def _get_content_type(converter: BaseConverter) -> str:
+    if JsonConverter is not None and isinstance(converter, JsonConverter):
+        content_type = "application/json"
+    elif ProtobufConverter is not None and isinstance(converter, ProtobufConverter):
+        content_type = "application/octet-stream"
+    else:
+        content_type = ""
+    return content_type
+
+
 async def route_handler(
     route: Route, request: web.Request, transport: WebAiohttpTransport
 ) -> web.Response:
@@ -68,20 +92,11 @@ async def route_handler(
         except Exception as error:
             raise _exception_to_response(error, transport.converter, cors_allow)
 
-        if JsonConverter is not None and isinstance(transport.converter, JsonConverter):
-            content_type = "application/json"
-        elif ProtobufConverter is not None and isinstance(
-            transport.converter, ProtobufConverter
-        ):
-            content_type = "application/octet-stream"
-        else:
-            content_type = ""
-
         return web.Response(
             body=result,
             status=201,
             headers=_get_cors_headers(cors_allow),
-            content_type=content_type,
+            content_type=_get_content_type(transport.converter),
         )
     # elif route.proto_cardinality == Cardinality.UNARY_STREAM:
     #     conn_id = request.get_header("connection-id")
@@ -216,7 +231,7 @@ async def start(self, routes: RoutesDict) -> None:
                             static_dir_index_handler, static_dir_path=static_dir_path
                         ),
                     ),
-                    web.static(static_dir_route, static_dir_path)
+                    web.static(static_dir_route, static_dir_path),
                 ]
             )
 
diff --git a/pyproject.toml b/pyproject.toml
index 449eb4c..a9b53b2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "modapp"
-version = "0.3.19"
+version = "0.3.20"
 description = ""
 authors = ["Vladyslav Hnatiuk <vhnatiuk@ukr.net>"]
 license = "MIT"