diff --git a/tests/nixos/github-flakes.nix b/tests/nixos/github-flakes.nix
index c6b3db96c..8175e807c 100644
--- a/tests/nixos/github-flakes.nix
+++ b/tests/nixos/github-flakes.nix
@@ -224,6 +224,10 @@ in
       hash = client.succeed(f"nix eval --no-trust-tarballs-from-git-forges --raw --expr '(fetchTree {info['url']}).narHash'")
       assert hash == info['locked']['narHash']
 
+      # Fetching with an incorrect NAR hash should fail.
+      out = client.fail(f"nix eval --no-trust-tarballs-from-git-forges --raw --expr '(fetchTree \"github:fancy-enterprise/private-flake/{info['revision']}?narHash=sha256-HsrRFZYg69qaVe/wDyWBYLeS6ca7ACEJg2Z%2BGpEFw4A%3D\").narHash' 2>&1")
+      assert "NAR hash mismatch in input" in out, "NAR hash check did not fail with the expected error"
+
       # Fetching without a narHash should succeed if trust-github is set and fail otherwise.
       client.succeed(f"nix eval --raw --expr 'builtins.fetchTree github:github:fancy-enterprise/private-flake/{info['revision']}'")
       out = client.fail(f"nix eval --no-trust-tarballs-from-git-forges --raw --expr 'builtins.fetchTree github:github:fancy-enterprise/private-flake/{info['revision']}' 2>&1")