diff --git a/slixmpp_omemo/__init__.py b/slixmpp_omemo/__init__.py
index b3fb4f4..1e0f314 100644
--- a/slixmpp_omemo/__init__.py
+++ b/slixmpp_omemo/__init__.py
@@ -593,6 +593,7 @@ class XEP_0384(BasePlugin):
             OMEMO_BASE_NS, self._device_id))
         # Don't error out. If it's not encrypted to us we don't need to send a
         # heartbeat.
+        prekey = False
         if key is not None:
             key = Key(key)
             prekey = key['prekey'] in TRUE_VALUES