diff --git a/pkgs/development/compilers/llvm/14/llvm/default.nix b/pkgs/development/compilers/llvm/14/llvm/default.nix
index d2059cc66ba2..05aac728b452 100644
--- a/pkgs/development/compilers/llvm/14/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/14/llvm/default.nix
@@ -209,6 +209,9 @@ in stdenv.mkDerivation (rec {
 
   checkTarget = "check-all";
 
+  # For the update script:
+  passthru.monorepoSrc = monorepoSrc;
+
   requiredSystemFeatures = [ "big-parallel" ];
   meta = llvm_meta // {
     homepage = "https://llvm.org/";
diff --git a/pkgs/development/compilers/llvm/update.sh b/pkgs/development/compilers/llvm/update.sh
index 603c603f275b..95ad356dbd9a 100755
--- a/pkgs/development/compilers/llvm/update.sh
+++ b/pkgs/development/compilers/llvm/update.sh
@@ -20,7 +20,11 @@ sed -Ei \
 
 readonly ATTRSET="llvmPackages_$VERSION_MAJOR"
 
-if [ "$VERSION_MAJOR" -ge "13" ]; then
+if [ "$VERSION_MAJOR" -ge "14" ]; then
+  readonly SOURCES=(
+    "llvm.monorepoSrc"
+  )
+elif [ "$VERSION_MAJOR" -eq "13" ]; then
   readonly SOURCES=(
     "llvm.src"
   )
@@ -43,7 +47,7 @@ fi
 for SOURCE in "${SOURCES[@]}"; do
   echo "Updating the hash of $SOURCE:"
   declare ATTR="$ATTRSET.$SOURCE"
-  declare OLD_HASH="$(nix eval -f . $ATTR.outputHash)"
+  declare OLD_HASH="$(nix --extra-experimental-features nix-command eval -f . $ATTR.outputHash)"
   declare NEW_HASH="\"$(nix-prefetch-url -A $ATTR)\""
   find "$DIR" -type f -exec sed -i "s/$OLD_HASH/$NEW_HASH/" {} +
 done