diff --git a/nix-builder/lib/checks.nix b/nix-builder/lib/checks.nix
index d5be9d5d..8f3d7044 100644
--- a/nix-builder/lib/checks.nix
+++ b/nix-builder/lib/checks.nix
@@ -103,6 +103,43 @@ let
           }
         ];
       };
+      testFlattenSystemsPtxasVersion = {
+        expr = flattenSystems [ (validVersion // { ptxasVersion = "13.4"; }) ];
+        expected = [
+          {
+            torchVersion = "2.13";
+            cudaVersion = "13.0";
+            ptxasVersion = "13.4";
+            system = "x86_64-linux";
+            bundleBuild = true;
+          }
+          {
+            torchVersion = "2.13";
+            cudaVersion = "13.0";
+            ptxasVersion = "13.4";
+            system = "aarch64-linux";
+            bundleBuild = true;
+          }
+        ];
+      };
+      testFlattenSystemsPtxasVersionPerSystem = {
+        expr = flattenSystems [ (validVersion // { ptxasVersion.aarch64-linux = "13.4"; }) ];
+        expected = [
+          {
+            torchVersion = "2.13";
+            cudaVersion = "13.0";
+            system = "x86_64-linux";
+            bundleBuild = true;
+          }
+          {
+            torchVersion = "2.13";
+            cudaVersion = "13.0";
+            ptxasVersion = "13.4";
+            system = "aarch64-linux";
+            bundleBuild = true;
+          }
+        ];
+      };
       testFlattenSystemsValidates = {
         expr = throws (flattenSystems [ (validVersion // { cudaVerison = "13.0"; }) ]);
         expected = true;
diff --git a/nix-builder/lib/mk-build-set.nix b/nix-builder/lib/mk-build-set.nix
index 199e0acb..2e14ace6 100644
--- a/nix-builder/lib/mk-build-set.nix
+++ b/nix-builder/lib/mk-build-set.nix
@@ -39,11 +39,14 @@ let
           self: super: {
             cuda_nvcc = super.cuda_nvcc.overrideAttrs (prevAttrs: {
               # Do this before the original postInstall, so that subsequent
-              # postInstall steps are applied.
+              # postInstall steps are applied. Since CUDA 13, nvvm is not
+              # part of cuda_nvcc anymore, but a separate libnvvm package.
               postInstall = ''
                 cp ${ptxasPackages.cuda_nvcc.src}/bin/ptxas $out/bin/ptxas
                 cp ${ptxasPackages.cuda_nvcc.src}/bin/nvlink $out/bin/nvlink
-                cp ${ptxasPackages.cuda_nvcc.src}/nvvm/bin/* $out/nvvm/bin/
+                if [ -d ${ptxasPackages.cuda_nvcc.src}/nvvm/bin ]; then
+                  cp ${ptxasPackages.cuda_nvcc.src}/nvvm/bin/* $out/nvvm/bin/
+                fi
               ''
               + prevAttrs.postInstall or "";
             });
diff --git a/nix-builder/lib/torch-version-utils.nix b/nix-builder/lib/torch-version-utils.nix
index 4614ca31..e9aa62b3 100644
--- a/nix-builder/lib/torch-version-utils.nix
+++ b/nix-builder/lib/torch-version-utils.nix
@@ -41,13 +41,37 @@ rec {
           version
       );
 
+  # `ptxasVersion` is either a version string that applies to all systems,
+  # or an attrset { <system> = <version>; } to override ptxas only on some
+  # systems. Resolve it for a single system; `null` means: use the ptxas
+  # from `cudaVersion`.
+  ptxasVersionForSystem =
+    version: system:
+    let
+      ptxasVersion = version.ptxasVersion or null;
+    in
+    if builtins.isAttrs ptxasVersion then ptxasVersion.${system} or null else ptxasVersion;
+
   # Expand { systems = [ a b ]; .. } to [ { system = a; ..} { system = b; .. } ]
   flattenSystems =
     versions:
     lib.foldl' (
       acc: version:
       acc
-      ++ map (system: (builtins.removeAttrs version [ "systems" ]) // { inherit system; }) version.systems
+      ++ map (
+        system:
+        let
+          ptxasVersion = ptxasVersionForSystem version system;
+        in
+        (builtins.removeAttrs version [
+          "systems"
+          "ptxasVersion"
+        ])
+        // {
+          inherit system;
+        }
+        // lib.optionalAttrs (ptxasVersion != null) { inherit ptxasVersion; }
+      ) version.systems
     ) [ ] (map validateTorchVersion versions);
 
   backend =
diff --git a/nix-builder/versions.nix b/nix-builder/versions.nix
index 5abf043a..12e8e305 100644
--- a/nix-builder/versions.nix
+++ b/nix-builder/versions.nix
@@ -30,6 +30,8 @@
   {
     torchVersion = "2.10";
     cudaVersion = "13.0";
+    # ptxas 13.0 segfaults on aarch64 compiling large sm90 kernels (flash-attn3).
+    ptxasVersion.aarch64-linux = "13.4";
     systems = [
       "x86_64-linux"
       "aarch64-linux"
@@ -83,6 +85,8 @@
   {
     torchVersion = "2.11";
     cudaVersion = "13.0";
+    # ptxas 13.0 segfaults on aarch64 compiling large sm90 kernels (flash-attn3).
+    ptxasVersion.aarch64-linux = "13.4";
     systems = [
       "x86_64-linux"
       "aarch64-linux"
@@ -152,6 +156,8 @@
   {
     torchVersion = "2.12";
     cudaVersion = "13.0";
+    # ptxas 13.0 segfaults on aarch64 compiling large sm90 kernels (flash-attn3).
+    ptxasVersion.aarch64-linux = "13.4";
     systems = [
       "x86_64-linux"
       "aarch64-linux"
@@ -216,6 +222,8 @@
   {
     torchVersion = "2.13";
     cudaVersion = "13.0";
+    # ptxas 13.0 segfaults on aarch64 compiling large sm90 kernels (flash-attn3).
+    ptxasVersion.aarch64-linux = "13.4";
     systems = [
       "x86_64-linux"
       "aarch64-linux"
@@ -283,6 +291,8 @@
   {
     torchVersion = "2.14";
     cudaVersion = "13.0";
+    # ptxas 13.0 segfaults on aarch64 compiling large sm90 kernels (flash-attn3).
+    ptxasVersion.aarch64-linux = "13.4";
     systems = [
       "x86_64-linux"
       "aarch64-linux"