diff --git a/pkgs/top-level/make-tarball.nix b/pkgs/top-level/make-tarball.nix
index 2e2489bd5c87..93a833c994fe 100644
--- a/pkgs/top-level/make-tarball.nix
+++ b/pkgs/top-level/make-tarball.nix
@@ -43,7 +43,7 @@ releaseTools.makeSourceTarball {
   checkPhase = ''
     # Run the regression tests in `lib'.
     res="$(nix-instantiate --eval-only --strict pkgs/lib/tests.nix)"
-    if test "$res" != "[]"; then
+    if test "$res" != "[ ]"; then
         echo "regression tests for lib failed, got: $res"
         exit 1
     fi