diff --git a/pkgs/stdenv/generic/setup.sh b/pkgs/stdenv/generic/setup.sh
index dbbe45e45f3..e4a77af199b 100644
--- a/pkgs/stdenv/generic/setup.sh
+++ b/pkgs/stdenv/generic/setup.sh
@@ -769,7 +769,7 @@ _defaultUnpack() {
         # We can't preserve hardlinks because they may have been
         # introduced by store optimization, which might break things
         # in the build.
-        cp -pr --reflink=auto "$fn" "$(stripHash "$fn")"
+        cp -pr --reflink=auto -- "$fn" "$(stripHash "$fn")"
 
     else