diff --git a/tests/overlay-local-store/check-post-init-inner.sh b/tests/overlay-local-store/check-post-init-inner.sh
index c7d1c70d4..2e7db2adc 100755
--- a/tests/overlay-local-store/check-post-init-inner.sh
+++ b/tests/overlay-local-store/check-post-init-inner.sh
@@ -62,7 +62,7 @@ nix-store --verify-path --store "$storeA" "$path"
 # Verifying path in merged-store
 nix-store --verify-path --store "$storeB" "$path"
 
-hashPart=$(echo $path | sed "s^$NIX_STORE_DIR/^^" | sed 's/-.*//')
+hashPart=$(echo $path | sed "s^${NIX_STORE_DIR:-/nix/store}/^^" | sed 's/-.*//')
 
 # Lower store can find from hash part
 [[ $(nix store --store $storeA path-from-hash-part $hashPart) == $path ]]
diff --git a/tests/overlay-local-store/common.sh b/tests/overlay-local-store/common.sh
index 686523e9c..ac4a59cd8 100644
--- a/tests/overlay-local-store/common.sh
+++ b/tests/overlay-local-store/common.sh
@@ -53,7 +53,7 @@ remountOverlayfs () {
 toRealPath () {
   storeDir=$1; shift
   storePath=$1; shift
-  echo $storeDir$(echo $storePath | sed "s^$NIX_STORE_DIR^^")
+  echo $storeDir$(echo $storePath | sed "s^${NIX_STORE_DIR:-/nix/store}^^")
 }
 
 initLowerStore () {