diff --git a/pkgs/comma/comma b/pkgs/comma/comma
index 5c347d6..ba5c6ae 100755
--- a/pkgs/comma/comma
+++ b/pkgs/comma/comma
@@ -30,4 +30,4 @@ if [ -z "$PROGRAM" ]; then
     exit 1
 fi
 
-nix shell "nixpkgs#$PROGRAM" -c "$@"
+nix shell "${COMMA_PKGS_FLAKE:-nixpkgs}#$PROGRAM" -c "$@"