diff --git a/pkgs/build-support/fetchmtn/default.nix b/pkgs/build-support/fetchmtn/default.nix
index 4aa134242aa7..de208b92193f 100644
--- a/pkgs/build-support/fetchmtn/default.nix
+++ b/pkgs/build-support/fetchmtn/default.nix
@@ -1,25 +1,24 @@
 # You can specify some extra mirrors and a cache DB via options
 {lib, stdenvNoCC, monotone, defaultDBMirrors ? [], cacheDB ? "./mtn-checkout.db"}:
-# dbs is a list of strings
-# each is an url for sync
 
-# selector is mtn selector, like h:org.example.branch
-#
-{name ? "mtn-checkout", dbs ? [], sha256
-, selector ? "h:" + branch, branch}:
+lib.fetchers.withNormalizedHash { } (
+  # dbs is a list of strings, each is an url for sync
+  # selector is mtn selector, like h:org.example.branch
+  {name ? "mtn-checkout", dbs ? []
+  , outputHash, outputHashAlgo
+  , selector ? "h:" + branch, branch}:
 
-stdenvNoCC.mkDerivation {
-  builder = ./builder.sh;
-  nativeBuildInputs = [monotone];
+  stdenvNoCC.mkDerivation {
+    builder = ./builder.sh;
+    nativeBuildInputs = [monotone];
 
-  outputHashAlgo = "sha256";
-  outputHashMode = "recursive";
-  outputHash = sha256;
+    inherit outputHash outputHashAlgo;
+    outputHashMode = "recursive";
 
-  dbs = defaultDBMirrors ++ dbs;
-  inherit branch cacheDB name selector;
+    dbs = defaultDBMirrors ++ dbs;
+    inherit branch cacheDB name selector;
 
-  impureEnvVars = lib.fetchers.proxyImpureEnvVars;
-
-}
+    impureEnvVars = lib.fetchers.proxyImpureEnvVars;
 
+  }
+)