diff --git a/modules/sasl/scram.py b/modules/sasl/scram.py
index 2f66e44d..ffe5a9f0 100644
--- a/modules/sasl/scram.py
+++ b/modules/sasl/scram.py
@@ -27,7 +27,7 @@ class SCRAMError(Exception):
     pass
 
 class SCRAM(object):
-    def __init__(self, algo, username, password):
+    def __init__(self, algo: str, username: str, password: str):
         if not algo in ALGORITHMS:
             raise ValueError("Unknown SCRAM algorithm '%s'" % algo)