diff --git a/lib/roman_numerals.dart b/lib/roman_numerals.dart
index f4666c1..abddc4d 100644
--- a/lib/roman_numerals.dart
+++ b/lib/roman_numerals.dart
@@ -1,5 +1,12 @@
 String integerToRoman(int number) {
-  const conversionRules = [(10, 'X'), (9, 'IX'), (5, 'V'), (4, 'IV'), (1, 'I')];
+  const conversionRules = [
+    (40, 'XL'),
+    (10, 'X'),
+    (9, 'IX'),
+    (5, 'V'),
+    (4, 'IV'),
+    (1, 'I'),
+  ];
 
   final result = StringBuffer();
   var remaining = number;