diff --git a/9-regular-expressions/15-regexp-catastrophic-backtracking/article.md b/9-regular-expressions/15-regexp-catastrophic-backtracking/article.md
index b6e1054fb..c1d4040f7 100644
--- a/9-regular-expressions/15-regexp-catastrophic-backtracking/article.md
+++ b/9-regular-expressions/15-regexp-catastrophic-backtracking/article.md
@@ -283,7 +283,7 @@ alert( "JavaScript".match(/(?=(\w+))\1Script/)); // null
 We can put a more complex regular expression into `pattern:(?=(\w+))\1` instead of `pattern:\w`, when we need to forbid backtracking for `pattern:+` after it.
 
 ```smart
-There's more about the relation between possessive quantifiers and lookahead in articles [Regex: Emulate Atomic Grouping (and Possessive Quantifiers) with LookAhead](http://instanceof.me/post/52245507631/regex-emulate-atomic-grouping-with-lookahead) and [Mimicking Atomic Groups](http://blog.stevenlevithan.com/archives/mimic-atomic-groups).
+There's more about the relation between possessive quantifiers and lookahead in articles [Regex: Emulate Atomic Grouping (and Possessive Quantifiers) with LookAhead](https://instanceof.me/post/52245507631/regex-emulate-atomic-grouping-with-lookahead) and [Mimicking Atomic Groups](https://blog.stevenlevithan.com/archives/mimic-atomic-groups).
 ```
 
 Let's rewrite the first example using lookahead to prevent backtracking: