diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index a414fc8..63e1a56 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -41,7 +41,7 @@ jobs:
     - name: Run server in background
       run: |
         misp-modules -l 127.0.0.1 -s 2>error.log &
-        sleep 5
+        sleep 3
     - name: Check if server is running
       run: |
         curl -sS localhost:6666/healthcheck
diff --git a/misp_modules/__init__.py b/misp_modules/__init__.py
index bdbd601..bd76f3a 100644
--- a/misp_modules/__init__.py
+++ b/misp_modules/__init__.py
@@ -39,6 +39,7 @@ import tornado.process
 from tornado.ioloop import IOLoop
 from tornado.concurrent import run_on_executor
 from concurrent.futures import ThreadPoolExecutor
+from pymisp import pymisp_json_default
 
 try:
     from .modules import *  # noqa
@@ -202,7 +203,7 @@ class QueryModule(tornado.web.RequestHandler):
             response = module.dict_handler(request=dict_payload)
         else:
             response = module.handler(q=json_payload)
-        return json.dumps(response)
+        return json.dumps(response, default=pymisp_json_default)
 
     @tornado.gen.coroutine
     def post(self):
@@ -303,6 +304,9 @@ def main():
                     return 1
             print(e)
             print("misp-modules might still be running.")
+        else:
+            log.exception(f"Could not listen on {args.listen}:{args.port}")
+            return 1
 
     log.info(f'MISP modules server started on {args.listen} port {args.port}')
     if args.test: