diff --git a/.git-blame-ignore-revs b/.git-blame-ignore-revs
index 5d3c35edb4d4..9156c6563ec7 100644
--- a/.git-blame-ignore-revs
+++ b/.git-blame-ignore-revs
@@ -193,6 +193,9 @@ cffc27daf06c77c0d76bc35d24b929cb9d68c3c9
 # nixos/kanidm: inherit lib, nixfmt
 8f18393d380079904d072007fb19dc64baef0a3a
 
+# fetchhg: format after refactoring with lib.extendMkDerivation and make overridable (#423539)
+34a5b1eb23129f8fb62c677e3760903f6d43228f
+
 # fetchurl: nixfmt-rfc-style
 ce21e97a1f20dee15da85c084f9d1148d84f853b