diff --git a/tests/v1/core/test_reset_prefix_cache_e2e.py b/tests/v1/core/test_reset_prefix_cache_e2e.py
index e543c30a156e..083fc3f34f54 100644
--- a/tests/v1/core/test_reset_prefix_cache_e2e.py
+++ b/tests/v1/core/test_reset_prefix_cache_e2e.py
@@ -11,7 +11,9 @@ PROMPTS = [
 ]
 
 
-def test_reset_prefix_cache_e2e():
+def test_reset_prefix_cache_e2e(monkeypatch):
+    # "spawn" is required for test to be deterministic
+    monkeypatch.setenv("VLLM_WORKER_MULTIPROC_METHOD", "spawn")
     engine_args = EngineArgs(
         model="Qwen/Qwen3-0.6B",
         gpu_memory_utilization=0.2,