diff --git a/tests/flakes.sh b/tests/flakes.sh
index 26ffd6a9f..da952d552 100644
--- a/tests/flakes.sh
+++ b/tests/flakes.sh
@@ -110,6 +110,10 @@ nix build -o $TEST_ROOT/result --flake-registry $registry $flake2:bar
 [[ -e $flake2/flake.lock ]]
 git -C $flake2 commit flake.lock -m 'Add flake.lock'
 
+# Rerunning the build should not change the lockfile.
+nix build -o $TEST_ROOT/result --flake-registry $registry $flake2:bar
+[[ -z $(git -C $flake2 diff) ]]
+
 # Now we should be able to build the flake in pure mode.
 nix build -o $TEST_ROOT/result --flake-registry $registry flake2:bar