diff --git a/src/infra/openclaw-exec-env.test.ts b/src/infra/openclaw-exec-env.test.ts
index 488fa1dd5ef..0951757876c 100644
--- a/src/infra/openclaw-exec-env.test.ts
+++ b/src/infra/openclaw-exec-env.test.ts
@@ -27,4 +27,20 @@ describe("ensureOpenClawExecMarkerOnProcess", () => {
     expect(ensureOpenClawExecMarkerOnProcess(env)).toBe(env);
     expect(env[OPENCLAW_CLI_ENV_VAR]).toBe(OPENCLAW_CLI_ENV_VALUE);
   });
+
+  it("defaults to mutating process.env when no env object is provided", () => {
+    const previous = process.env[OPENCLAW_CLI_ENV_VAR];
+    delete process.env[OPENCLAW_CLI_ENV_VAR];
+
+    try {
+      expect(ensureOpenClawExecMarkerOnProcess()).toBe(process.env);
+      expect(process.env[OPENCLAW_CLI_ENV_VAR]).toBe(OPENCLAW_CLI_ENV_VALUE);
+    } finally {
+      if (previous === undefined) {
+        delete process.env[OPENCLAW_CLI_ENV_VAR];
+      } else {
+        process.env[OPENCLAW_CLI_ENV_VAR] = previous;
+      }
+    }
+  });
 });