diff --git a/lib/string_calculator.dart b/lib/string_calculator.dart
index 2bb4e23..934878c 100644
--- a/lib/string_calculator.dart
+++ b/lib/string_calculator.dart
@@ -27,7 +27,7 @@ class StringCalculator {
     if (numbers.startsWith('//')) {
       // Bug 4: Custom delimiter not actually used
       final parts = numbers.split('\n');
-      // delimiter = parts[0].substring(2); // BUG: Commented out - never extracts delimiter!
+      delimiter = parts[0].substring(2); // Fixed: Extract custom delimiter
       numbersToProcess = parts.skip(1).join('\n');
     }