diff --git a/slixmpp_omemo/__init__.py b/slixmpp_omemo/__init__.py
index e736017..b885d8b 100644
--- a/slixmpp_omemo/__init__.py
+++ b/slixmpp_omemo/__init__.py
@@ -557,7 +557,7 @@ class XEP_0384(BasePlugin):
         receiving_chain_lengths = self._chain_lengths(jid).get('receiving', [])
         lengths = map(lambda d_l: d_l[1], receiving_chain_lengths)
         min_length = reduce(lambda x, d_l: min(x, d_l[1]), receiving_chain_lengths, 0) == -1
-        return min_length or max(lengths, default=0) > self.heartbeat_after
+        return min_length == -1 or max(lengths, default=0) > self.heartbeat_after
 
     async def make_heartbeat(self, jid: JID) -> Message:
         """