diff --git a/pkgs/development/python-modules/materialx/default.nix b/pkgs/development/python-modules/materialx/default.nix
index 5d2c09dfef7f..43b766a5662f 100644
--- a/pkgs/development/python-modules/materialx/default.nix
+++ b/pkgs/development/python-modules/materialx/default.nix
@@ -18,6 +18,9 @@ buildPythonPackage rec {
   pname = "materialx";
   version = "1.38.10";
 
+  # nixpkgs-update: no auto update
+  # Updates are disabled due to API breakage in 1.39+ that breaks almost all
+  # consumers.
   src = fetchFromGitHub {
     owner = "AcademySoftwareFoundation";
     repo = "MaterialX";