diff --git a/pkgs/development/compilers/llvm/common/default.nix b/pkgs/development/compilers/llvm/common/default.nix
index 227f8db5f652..c56a8fee1476 100644
--- a/pkgs/development/compilers/llvm/common/default.nix
+++ b/pkgs/development/compilers/llvm/common/default.nix
@@ -515,7 +515,17 @@ let
       # we need to reintroduce `outputSpecified` to get the expected behavior e.g. of lib.get*
       llvm = tools.libllvm;
 
-      tblgen = callPackage ./tblgen.nix { };
+      tblgen = callPackage ./tblgen.nix {
+        patches = builtins.filter
+          # Crude method to drop polly patches if present, they're not needed for tblgen.
+          (p: (!lib.hasInfix "-polly" p)) tools.libllvm.patches;
+        clangPatches = [
+          # Would take tools.libclang.patches, but this introduces a cycle due
+          # to replacements depending on the llvm outpath (e.g. the LLVMgold patch).
+          # So take the only patch known to be necessary.
+          (metadata.getVersionFile "clang/gnu-install-dirs.patch")
+        ];
+      };
 
       libclang = callPackage ./clang {
         patches =
diff --git a/pkgs/development/compilers/llvm/common/tblgen.nix b/pkgs/development/compilers/llvm/common/tblgen.nix
index fe213e00b847..49cbcb0af2ca 100644
--- a/pkgs/development/compilers/llvm/common/tblgen.nix
+++ b/pkgs/development/compilers/llvm/common/tblgen.nix
@@ -12,6 +12,7 @@
   src ? null,
   stdenv,
   version,
+  clangPatches,
 }:
 
 let
@@ -60,6 +61,17 @@ let
     src = src';
     sourceRoot = "${src.name}/llvm";
 
+    postPatch = ''
+      (
+        cd ../clang
+        chmod u+rwX -R .
+        for p in ${toString clangPatches}
+        do
+          patch -p1 < $p
+        done
+      )
+    '';
+
     nativeBuildInputs = [
       cmake
       ninja
@@ -69,12 +81,16 @@ let
     cmakeFlags = [
       # Projects with tablegen-like tools.
       "-DLLVM_ENABLE_PROJECTS=${
-        lib.concatStringsSep ";" [
-          "llvm"
-          "clang"
-          "clang-tools-extra"
-          "mlir"
-        ]
+        lib.concatStringsSep ";" (
+          [
+            "llvm"
+            "clang"
+            "clang-tools-extra"
+          ]
+          ++ lib.optionals (lib.versionAtLeast release_version "16") [
+            "mlir"
+          ]
+        )
       }"
     ] ++ devExtraCmakeFlags;
 
@@ -82,13 +98,19 @@ let
     ninjaFlags =
       [
         "clang-tblgen"
-        "clang-tidy-confusable-chars-gen"
         "llvm-tblgen"
+      ]
+      ++ lib.optionals (lib.versionAtLeast release_version "15") [
+        "clang-tidy-confusable-chars-gen"
+      ]
+      ++ lib.optionals (lib.versionAtLeast release_version "16") [
         "mlir-tblgen"
       ]
-      ++ lib.optionals (lib.versionOlder release_version "20") [
-        "clang-pseudo-gen" # Removed in LLVM 20 @ ed8f78827895050442f544edef2933a60d4a7935.
-      ];
+      ++
+        lib.optionals ((lib.versionAtLeast release_version "15") && (lib.versionOlder release_version "20"))
+          [
+            "clang-pseudo-gen" # Removed in LLVM 20 @ ed8f78827895050442f544edef2933a60d4a7935.
+          ];
 
     installPhase = ''
       mkdir -p $out