diff --git a/MutualRecursion.py b/MutualRecursion.py
index b88b9eced08eff33a1e449a462fae02a74c5c00d..066f502e566c2c919b47d8c904e3004a0e70a7cb 100755
--- a/MutualRecursion.py
+++ b/MutualRecursion.py
@@ -93,10 +93,10 @@ def divide(left_expression, right_expression):
 
 
 operator_map = {
-    "+": add,
-    "-": subtract,
-    "*": multiply,
-    "/": divide
+    '+': add,
+    '-': subtract,
+    '*': multiply,
+    '/': divide
 }