diff --git a/ci/build.py b/ci/build.py
index 7de4e1156..de9eb9d84 100755
--- a/ci/build.py
+++ b/ci/build.py
@@ -10,6 +10,8 @@
 import sys
 import contextlib
 
+assert list(map(int, sys.version.split(" ")[0].split("."))) > [3, 9, 0]
+
 sys.path.insert(1, Path(__file__).parents[1].as_posix())
 
 from ci.lib.runner import ArgparseActionList, TestConfig, matrix_product
diff --git a/ci/examples/blk.py b/ci/examples/blk.py
index 830741687..7df91eeaf 100755
--- a/ci/examples/blk.py
+++ b/ci/examples/blk.py
@@ -10,6 +10,8 @@
 import tempfile
 import types
 
+assert list(map(int, sys.version.split(" ")[0].split("."))) > [3, 9, 0]
+
 sys.path.insert(1, Path(__file__).parents[2].as_posix())
 
 from ci.lib.backends import *
diff --git a/ci/examples/echo_server.py b/ci/examples/echo_server.py
index 517a27a8a..1d9e860ed 100755
--- a/ci/examples/echo_server.py
+++ b/ci/examples/echo_server.py
@@ -7,6 +7,8 @@
 from pathlib import Path
 import sys
 
+assert list(map(int, sys.version.split(" ")[0].split("."))) > [3, 9, 0]
+
 sys.path.insert(1, Path(__file__).parents[2].as_posix())
 
 from ci.lib.backends import *
diff --git a/ci/examples/i2c.py b/ci/examples/i2c.py
index d794f8922..a0daeb308 100755
--- a/ci/examples/i2c.py
+++ b/ci/examples/i2c.py
@@ -6,6 +6,8 @@
 from pathlib import Path
 import sys
 
+assert list(map(int, sys.version.split(" ")[0].split("."))) > [3, 9, 0]
+
 sys.path.insert(1, Path(__file__).parents[2].as_posix())
 
 from ci.lib.backends import *
diff --git a/ci/examples/i2c_bus_scan.py b/ci/examples/i2c_bus_scan.py
index 59ac23b23..0b0295d5f 100755
--- a/ci/examples/i2c_bus_scan.py
+++ b/ci/examples/i2c_bus_scan.py
@@ -6,6 +6,8 @@
 from pathlib import Path
 import sys
 
+assert list(map(int, sys.version.split(" ")[0].split("."))) > [3, 9, 0]
+
 sys.path.insert(1, Path(__file__).parents[2].as_posix())
 
 from ci.lib.backends import *
diff --git a/ci/examples/serial.py b/ci/examples/serial.py
index 7253bb6ac..e6fbe7e6d 100755
--- a/ci/examples/serial.py
+++ b/ci/examples/serial.py
@@ -6,6 +6,8 @@
 from pathlib import Path
 import sys
 
+assert list(map(int, sys.version.split(" ")[0].split("."))) > [3, 9, 0]
+
 sys.path.insert(1, Path(__file__).parents[2].as_posix())
 
 from ci.lib.backends import *
diff --git a/ci/examples/timer.py b/ci/examples/timer.py
index cbd1ed97e..f2b0de161 100755
--- a/ci/examples/timer.py
+++ b/ci/examples/timer.py
@@ -6,6 +6,8 @@
 from pathlib import Path
 import sys
 
+assert list(map(int, sys.version.split(" ")[0].split("."))) > [3, 9, 0]
+
 sys.path.insert(1, Path(__file__).parents[2].as_posix())
 
 from ci.lib.backends import *
diff --git a/ci/run.py b/ci/run.py
index ba8621cb1..4f554a182 100755
--- a/ci/run.py
+++ b/ci/run.py
@@ -7,6 +7,8 @@
 from pathlib import Path
 import sys
 
+assert list(map(int, sys.version.split(" ")[0].split("."))) > [3, 9, 0]
+
 sys.path.insert(1, Path(__file__).parents[1].as_posix())
 
 from ci.common import TestConfig, backend_fn
diff --git a/flake.lock b/flake.lock
index 622eca798..cd5a2fb38 100644
--- a/flake.lock
+++ b/flake.lock
@@ -100,9 +100,26 @@
         "type": "github"
       }
     },
+    "python39": {
+      "locked": {
+        "lastModified": 1742943473,
+        "narHash": "sha256-u7+CYuAuCiJH3scDvMV9oj3p22ygnFhTXUefXUgd/LI=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c5dd43934613ae0f8ff37c59f61c507c2e8f980d",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c5dd43934613ae0f8ff37c59f61c507c2e8f980d",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "nixpkgs": "nixpkgs",
+        "python39": "python39",
         "sdfgen": "sdfgen",
         "zig-overlay": "zig-overlay_2"
       }
diff --git a/flake.nix b/flake.nix
index 946372f22..b5133006e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -7,6 +7,8 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
+    # Python 3.9 is not in the official repo anymore
+    python39.url = "github:NixOS/nixpkgs/c5dd43934613ae0f8ff37c59f61c507c2e8f980d";
     zig-overlay.url = "github:mitchellh/zig-overlay";
     zig-overlay.inputs.nixpkgs.follows = "nixpkgs";
     sdfgen.url = "github:au-ts/microkit_sdf_gen/0.28.1";
@@ -16,6 +18,7 @@
   outputs =
     {
       nixpkgs,
+      python39,
       zig-overlay,
       sdfgen,
       ...
@@ -39,13 +42,16 @@
           pkgs = import nixpkgs {
             inherit system;
           };
+          pkgs39 = import python39 {
+            inherit system;
+          };
 
           llvm = pkgs.llvmPackages_18;
           zig = zig-overlay.packages.${system}."0.15.1";
 
           pysdfgen = sdfgen.packages.${system}.pysdfgen.override {
             zig = zig;
-            pythonPackages = pkgs.python312Packages;
+            pythonPackages = pkgs39.python39Packages;
           };
 
           clang-complete = (pkgs.symlinkJoin {
@@ -73,9 +79,16 @@
 
           genmc = pkgs.callPackage ./ci/genmc/nix/package.nix { inherit clang-complete; llvm = pkgs.llvmPackages_20.llvm; };
 
-          pythonTool = pkgs.python312.withPackages (ps: [
+          pythonTool = pkgs39.python39.withPackages (ps: [
             pysdfgen
           ]);
+          ## Fixup python and python3 resolving
+          pythonShim = pkgs.writeShellScriptBin "python" ''
+            exec ${pythonTool}/bin/python3 "$@"
+          '';
+          python3Shim = pkgs.writeShellScriptBin "python3" ''
+            exec ${pythonTool}/bin/python3 "$@"
+          '';
         in
         {
           genmc = pkgs.mkShell rec {
@@ -131,6 +144,8 @@
               llvm.libllvm
               dtc
               pythonTool
+              pythonShim
+              python3Shim
             ];
 
             # To avoid Nix adding compiler flags that are not available on a freestanding