diff --git a/rust/crates/rusty-claude-cli/src/main.rs b/rust/crates/rusty-claude-cli/src/main.rs
index e5d55e4..918fbfb 100644
--- a/rust/crates/rusty-claude-cli/src/main.rs
+++ b/rust/crates/rusty-claude-cli/src/main.rs
@@ -10816,6 +10816,9 @@ UU conflicted.rs",
 
     #[test]
     fn build_runtime_runs_plugin_lifecycle_init_and_shutdown() {
+        // Serialize access to process-wide env vars so parallel tests that
+        // set/remove ANTHROPIC_API_KEY do not race with this test.
+        let _guard = env_lock();
         let config_home = temp_dir();
         // Inject a dummy API key so runtime construction succeeds without real credentials.
         // This test only exercises plugin lifecycle (init/shutdown), never calls the API.