diff --git a/tests/nixos/fetchers-substitute.nix b/tests/nixos/fetchers-substitute.nix
index dc3bb7c02..5363f8e72 100644
--- a/tests/nixos/fetchers-substitute.nix
+++ b/tests/nixos/fetchers-substitute.nix
@@ -47,6 +47,7 @@
     { nodes }: # python
     ''
       import json
+      import os
 
       start_all()
 
@@ -118,9 +119,8 @@
 
       # Get the NAR hash of the unpacked tarball in SRI format
       path_info_json = substituter.succeed(f"nix path-info --json-format 2 --json {tarball_store_path}").strip()
-      path_info_dict = json.loads(path_info_json)
-      # nix path-info returns a dict with store paths as keys
-      narHash_obj = path_info_dict[tarball_store_path]["narHash"]
+      path_info_dict = json.loads(path_info_json)["info"]
+      narHash_obj = path_info_dict[os.path.basename(tarball_store_path)]["narHash"]
       # Convert from structured format {"algorithm": "sha256", "format": "base16", "hash": "..."} to SRI string
       tarball_hash_sri = substituter.succeed(f"nix hash convert --to sri {narHash_obj['algorithm']}:{narHash_obj['hash']}").strip()
       print(f"Tarball NAR hash (SRI): {tarball_hash_sri}")