diff --git a/slixmpp_omemo/__init__.py b/slixmpp_omemo/__init__.py
index 80de0a9..927dcc5 100644
--- a/slixmpp_omemo/__init__.py
+++ b/slixmpp_omemo/__init__.py
@@ -82,7 +82,7 @@ def _load_device_id(data_dir: str) -> int:
 
 def fp_from_ik(identity_key: bytes) -> str:
     """Convert identityKey to a string representation (fingerprint)"""
-    return ":".join("{:02X}".format(octet) for octet in identity_key)
+    return "".join("{:02x}".format(octet) for octet in identity_key)
 
 
 def _parse_bundle(backend: Backend, bundle: Bundle) -> ExtendedPublicBundle: