diff --git a/exercises/isogram/isogram.py b/exercises/isogram/isogram.py
index 7b0ccf92606..98b31c5b00e 100644
--- a/exercises/isogram/isogram.py
+++ b/exercises/isogram/isogram.py
@@ -1,2 +1,2 @@
-def is_isogram():
+def is_isogram(string):
     pass