diff --git a/mitama/app/app.py b/mitama/app/app.py
index 2008a0f..4eb28e3 100644
--- a/mitama/app/app.py
+++ b/mitama/app/app.py
@@ -154,11 +154,24 @@ def _session_middleware():
     from mitama.app import Middleware
     from mitama.app.http.session import EncryptedCookieStorage
 
+    if "MITAMA_SESSION_KEY" in os.environ:
+        session_key = os.environ["MITAMA_SESSION_KEY"]
+    elif os.path.exists(".tmp/MITAMA_SESSION_KEY"):
+        with open(".tmp/MITAMA_SESSION_KEY", "r") as f:
+            session_key = f.read()
+    else:
+        key = fernet.Fernet.generate_key()
+        session_key = base64.urlsafe_b64encode(key).decode("utf-8")
+        if not os.path.exists(".tmp"):
+            os.mkdir(".tmp")
+        with open(".tmp/MITAMA_SESSION_KEY", "w") as f:
+            f.write(session_key)
+
     class SessionMiddleware(Middleware):
-        fernet_key = fernet.Fernet.generate_key()
+        fernet_key = session_key
 
         def __init__(self):
-            secret_key = base64.urlsafe_b64decode(self.fernet_key)
+            secret_key = base64.urlsafe_b64decode(self.fernet_key.encode("utf-8"))
             cookie_storage = EncryptedCookieStorage(secret_key)
             self.storage = cookie_storage
 
diff --git a/mitama/app/http/session.py b/mitama/app/http/session.py
index 5130ecb..4cb5137 100644
--- a/mitama/app/http/session.py
+++ b/mitama/app/http/session.py
@@ -106,9 +106,9 @@ def __init__(
         self._encoder = encoder
         self._decoder = decoder
         if isinstance(secret_key, str):
-            pass
+            secret_key = secret_key.encode("utf-8")
         elif isinstance(secret_key, (bytes, bytearray)):
-            secret_key = base64.urlsafe_b64encode(secret_key)
+            pass
         self._fernet = fernet.Fernet(secret_key)
 
     @property
diff --git a/tests/test_apps/uwsgi.ini b/tests/test_apps/uwsgi.ini
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_apps/uwsgi.py b/tests/test_apps/uwsgi.py
new file mode 100644
index 0000000..7923ba2
--- /dev/null
+++ b/tests/test_apps/uwsgi.py
@@ -0,0 +1,14 @@
+#!/usr/bin/python
+
+"""
+uwsgi --http=0.0.0.0:8080 --wsgi-file=/path/to/this --callable=app.wsgi
+"""
+import os
+
+from mitama.app import AppRegistry, _MainApp
+
+PROJECT_DIR = os.path.dirname(__file__)
+os.chdir(PROJECT_DIR)
+app_registry = AppRegistry()
+app_registry.load_config()
+app = _MainApp(app_registry)