diff --git a/solve.py b/solve.py
index 36366fc..347e14e 100644
--- a/solve.py
+++ b/solve.py
@@ -133,7 +133,7 @@ def main_loop():
                 all_positional_letters.append(positional_letters)
                 all_non_positional_letters.append(non_positional_letters)
                 break
-        if all([letter.isupper for letter in letters]):
+        if all([letter.isupper() for letter in letters]):
             print("WIN")
             break
     else: