diff --git a/pkgs/development/libraries/py3c/default.nix b/pkgs/development/libraries/py3c/default.nix
index eec051f0cc1c..e46d01d0627a 100644
--- a/pkgs/development/libraries/py3c/default.nix
+++ b/pkgs/development/libraries/py3c/default.nix
@@ -11,7 +11,9 @@ stdenv.mkDerivation rec {
     sha256 = "04i2z7hrig78clc59q3i1z2hh24g7z1bfvxznlzxv00d4s57nhpi";
   };
 
-  postPatch = lib.optionalString stdenv.cc.isClang ''
+  postPatch = ''
+    # clang and gcc-11 complain about 'register' keywords used by
+    # python-2.7. Let's avoid blanket -Werror.
     substituteInPlace test/setup.py \
       --replace "'-Werror', " ""
   '';