diff --git a/pkgs/by-name/op/openhmd/package.nix b/pkgs/by-name/op/openhmd/package.nix
index 01fc1d072edf..6795d1aa8563 100644
--- a/pkgs/by-name/op/openhmd/package.nix
+++ b/pkgs/by-name/op/openhmd/package.nix
@@ -26,6 +26,13 @@ stdenv.mkDerivation rec {
     sha256 = "1hkpdl4zgycag5k8njvqpx01apxmm8m8pvhlsxgxpqiqy9a38ccg";
   };
 
+  # substitute for CMake 4 compat
+  # "OpenHMD is currently NOT ACTIVELY MAINTAINED" in upstream README
+  postPatch = ''
+    substituteInPlace CMakeLists.txt \
+      --replace-fail "cmake_minimum_required(VERSION 3.1)" "cmake_minimum_required(VERSION 3.10)"
+  '';
+
   nativeBuildInputs = [
     cmake
     pkg-config