diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 13a25f86520..328358c6e90 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -10320,6 +10320,9 @@ in
   gcc9Stdenv = overrideCC gccStdenv buildPackages.gcc9;
   gcc10Stdenv = overrideCC gccStdenv buildPackages.gcc10;
 
+  # This is not intended for use in nixpkgs but for providing a faster-running
+  # compiler to nixpkgs users by building gcc with reproducibility-breaking
+  # profile-guided optimizations
   fastStdenv = overrideCC gccStdenv (wrapNonDeterministicGcc gccStdenv buildPackages.gcc10);
 
   wrapCCMulti = cc: