diff --git a/slixmpp_omemo/__init__.py b/slixmpp_omemo/__init__.py
index 15a9699..a60ebb2 100644
--- a/slixmpp_omemo/__init__.py
+++ b/slixmpp_omemo/__init__.py
@@ -641,8 +641,8 @@ class XEP_0384(BasePlugin):
 
         return await self._omemo().getTrustForJID(jid.bare)
 
-    @classmethod
-    def is_encrypted(cls, msg: Message) -> bool:
+    @staticmethod
+    def is_encrypted(msg: Message) -> bool:
         return msg.xml.find('{%s}encrypted' % OMEMO_BASE_NS) is not None
 
     async def decrypt_message(