diff --git a/tests/build-remote.sh b/tests/build-remote.sh
index 78e12b477..d2a2132c1 100644
--- a/tests/build-remote.sh
+++ b/tests/build-remote.sh
@@ -1,6 +1,7 @@
 requireSandboxSupport
 [[ $busybox =~ busybox ]] || skipTest "no busybox"
 
+# Avoid store dir being inside sandbox build-dir
 unset NIX_STORE_DIR
 unset NIX_STATE_DIR
 
diff --git a/tests/supplementary-groups.sh b/tests/supplementary-groups.sh
index 47c6ef605..474ba7503 100644
--- a/tests/supplementary-groups.sh
+++ b/tests/supplementary-groups.sh
@@ -5,6 +5,10 @@ requireSandboxSupport
 if ! command -p -v unshare; then skipTest "Need unshare"; fi
 needLocalStore "The test uses --store always so we would just be bypassing the daemon"
 
+# Avoid store dir being inside sandbox build-dir
+unset NIX_STORE_DIR
+unset NIX_STATE_DIR
+
 unshare --mount --map-root-user bash <<EOF
   source common.sh