diff --git a/pkgs/by-name/cg/cgt-calc/package.nix b/pkgs/by-name/cg/cgt-calc/package.nix
index 9cb0f8732e9a..5e3a468d83f5 100644
--- a/pkgs/by-name/cg/cgt-calc/package.nix
+++ b/pkgs/by-name/cg/cgt-calc/package.nix
@@ -27,6 +27,8 @@ python3Packages.buildPythonApplication (finalAttrs: {
   ];
 
   pythonRelaxDeps = [
+    # The built wheel holds an upper bound requirement for the version of this
+    # dependenceis, while pyproject.toml doesn't.
     "defusedxml"
   ];