diff --git a/tests/entrypoints/weight_transfer/test_weight_transfer_llm.py b/tests/entrypoints/weight_transfer/test_weight_transfer_llm.py
index 9f2309c76..cd13aca7e 100644
--- a/tests/entrypoints/weight_transfer/test_weight_transfer_llm.py
+++ b/tests/entrypoints/weight_transfer/test_weight_transfer_llm.py
@@ -124,6 +124,8 @@ def test_init_weight_transfer_engine_calls_engine():
     if torch.cuda.device_count() < 1:
         pytest.skip("Need at least 1 GPU for this test")
 
+    # Run in-process so mock.patch works (spawn won't inherit the mock)
+    os.environ["VLLM_ENABLE_V1_MULTIPROCESSING"] = "0"
     # Enable insecure serialization to allow pickling functions for collective_rpc
     os.environ["VLLM_ALLOW_INSECURE_SERIALIZATION"] = "1"
 
@@ -171,6 +173,8 @@ def test_update_weights_calls_engine():
     if torch.cuda.device_count() < 1:
         pytest.skip("Need at least 1 GPU for this test")
 
+    # Run in-process so mock.patch works (spawn won't inherit the mock)
+    os.environ["VLLM_ENABLE_V1_MULTIPROCESSING"] = "0"
     # Enable insecure serialization to allow pickling functions for collective_rpc
     os.environ["VLLM_ALLOW_INSECURE_SERIALIZATION"] = "1"
 
@@ -228,6 +232,8 @@ def test_full_weight_transfer_flow():
     if torch.cuda.device_count() < 1:
         pytest.skip("Need at least 1 GPU for this test")
 
+    # Run in-process so mock.patch works (spawn won't inherit the mock)
+    os.environ["VLLM_ENABLE_V1_MULTIPROCESSING"] = "0"
     # Enable insecure serialization to allow pickling functions for collective_rpc
     os.environ["VLLM_ALLOW_INSECURE_SERIALIZATION"] = "1"