diff --git a/iscc_core/constants.py b/iscc_core/constants.py
index 7a221d2..5b66995 100644
--- a/iscc_core/constants.py
+++ b/iscc_core/constants.py
@@ -166,7 +166,7 @@ class MULTIBASE(str, enum.Enum):
     base64url = "u"
 
 
-"""Possible combinations of ISCC units for the first 3 components of MT.ISCC"""
+#: Possible combinations of ISCC units for the first 3 components of MT.ISCC
 UNITS = (
     tuple(),
     (MT.CONTENT,),