diff --git a/pkgs/by-name/ni/nixfmt/generated-package.nix b/pkgs/by-name/ni/nixfmt/generated-package.nix
index fc2566739ac9..15d12a654017 100644
--- a/pkgs/by-name/ni/nixfmt/generated-package.nix
+++ b/pkgs/by-name/ni/nixfmt/generated-package.nix
@@ -5,6 +5,7 @@
   base,
   bytestring,
   cmdargs,
+  containers,
   directory,
   fetchzip,
   file-embed,
@@ -23,15 +24,16 @@
 }:
 mkDerivation {
   pname = "nixfmt";
-  version = "1.1.0";
+  version = "1.2.0";
   src = fetchzip {
-    url = "https://github.com/nixos/nixfmt/archive/v1.1.0.tar.gz";
-    sha256 = "19sydkdw1579qmvzx0zq06s23bm6m6l9wp1kvsfhxawk8pkz2pc2";
+    url = "https://github.com/nixos/nixfmt/archive/v1.2.0.tar.gz";
+    sha256 = "1qvj1sddh7bgggqnj7cnhvfh4iz1pwzc9a9awc1g7y349yvpwad3";
   };
   isLibrary = true;
   isExecutable = true;
   libraryHaskellDepends = [
     base
+    containers
     megaparsec
     mtl
     parser-combinators
diff --git a/pkgs/by-name/ni/nixfmt/update.sh b/pkgs/by-name/ni/nixfmt/update.sh
index 3a44a0c6279a..f6890b115ef2 100755
--- a/pkgs/by-name/ni/nixfmt/update.sh
+++ b/pkgs/by-name/ni/nixfmt/update.sh
@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p cabal2nix curl jq
+#!nix-shell --pure -i bash -p cabal2nix curl cacert jq nix
 #
 # This script will update the nixfmt derivation to the latest version using
 # cabal2nix.
@@ -24,4 +24,7 @@ cabal2nix --jailbreak \
   "https://github.com/nixos/nixfmt/archive/${release_tag}.tar.gz" \
   >> "$derivation_file"
 
+nix-shell "$script_dir/../../../../" \
+  --run "treefmt --no-cache $derivation_file"
+
 echo "Finished."