diff --git a/tests/process-global/cleanLinuxHopperRuntime.test.ts b/tests/process-global/cleanLinuxHopperRuntime.test.ts
index d356f5abf..f6b9fc677 100644
--- a/tests/process-global/cleanLinuxHopperRuntime.test.ts
+++ b/tests/process-global/cleanLinuxHopperRuntime.test.ts
@@ -30,6 +30,9 @@ it
       await chmod(launcher, 0o700);
       await symlink(launcher, alternate);
     }
+    // A rejection must come from the fixture we are about to launch. An
+    // existing Xvfb would otherwise mask a broken executable-identity check.
+    await assertCleanLinuxHopperRuntime(alternateMode ? [launcher] : []);
     const command = alternateMode ? alternate : process.execPath;
     const arguments_ = alternateMode ? ["30"] : ["-e", childCode];
     const parentCode = `