diff --git a/tests/test_all_protocols_binary_field.py b/tests/test_all_protocols_binary_field.py
index e75e141..1f0a20a 100644
--- a/tests/test_all_protocols_binary_field.py
+++ b/tests/test_all_protocols_binary_field.py
@@ -3,6 +3,7 @@
 import sys
 import time
 import traceback
+import multiprocessing
 from multiprocessing import Process
 
 import pytest
@@ -25,6 +26,7 @@
     make_client as make_rpc_client
 from thriftpy2.transport import TBufferedTransportFactory, TCyMemoryBuffer
 
+multiprocessing.set_start_method("fork", force=True)
 
 if sys.platform == "win32":
     pytest.skip("requires fork", allow_module_level=True)
diff --git a/tests/test_apache_json.py b/tests/test_apache_json.py
index 85844e1..efc4012 100644
--- a/tests/test_apache_json.py
+++ b/tests/test_apache_json.py
@@ -4,6 +4,7 @@
 import json
 import sys
 import time
+import multiprocessing
 from multiprocessing import Process
 
 import pytest
@@ -19,6 +20,8 @@
 from thriftpy2.transport import TMemoryBuffer
 from thriftpy2.transport.buffered import TBufferedTransportFactory
 
+multiprocessing.set_start_method("fork", force=True)
+
 
 def recursive_vars(obj):
     if isinstance(obj, six.string_types):
diff --git a/tests/test_buffered_transport.py b/tests/test_buffered_transport.py
index 69cd715..08d4499 100644
--- a/tests/test_buffered_transport.py
+++ b/tests/test_buffered_transport.py
@@ -19,6 +19,8 @@
 from thriftpy2._compat import CYTHON
 logging.basicConfig(level=logging.INFO)
 
+multiprocessing.set_start_method("fork", force=True)
+
 addressbook = thriftpy2.load(path.join(path.dirname(__file__),
                                        "addressbook.thrift"))
 
diff --git a/tests/test_http.py b/tests/test_http.py
index 6d7493a..8ee65fd 100644
--- a/tests/test_http.py
+++ b/tests/test_http.py
@@ -18,6 +18,8 @@
 from thriftpy2.http import make_server, make_client, client_context, THttpHeaderFactory  # noqa
 from thriftpy2.thrift import TApplicationException  # noqa
 
+multiprocessing.set_start_method("fork", force=True)
+
 addressbook = thriftpy2.load(os.path.join(os.path.dirname(__file__),
                                           "addressbook.thrift"))
 
diff --git a/tests/test_multiplexed.py b/tests/test_multiplexed.py
index 3f38abf..be6ab54 100644
--- a/tests/test_multiplexed.py
+++ b/tests/test_multiplexed.py
@@ -20,6 +20,8 @@
 from thriftpy2.transport import TBufferedTransportFactory, TServerSocket
 
 
+multiprocessing.set_start_method("fork", force=True)
+
 if sys.platform == "win32":
     pytest.skip("requires fork", allow_module_level=True)
 
diff --git a/tests/test_oneway.py b/tests/test_oneway.py
index fcf88ba..afeb0a2 100644
--- a/tests/test_oneway.py
+++ b/tests/test_oneway.py
@@ -8,6 +8,8 @@
 from thriftpy2.rpc import make_client, make_server
 
 
+multiprocessing.set_start_method("fork", force=True)
+
 if sys.platform == "win32":
     pytest.skip("requires fork", allow_module_level=True)
 
diff --git a/tests/test_protocol_cybinary.py b/tests/test_protocol_cybinary.py
index 4bc8f7e..7725d11 100644
--- a/tests/test_protocol_cybinary.py
+++ b/tests/test_protocol_cybinary.py
@@ -19,6 +19,8 @@
 else:
     pytest.skip("cython not enabled.", allow_module_level=True)
 
+multiprocessing.set_start_method("fork", force=True)
+
 
 class TItem(TPayload):
     thrift_spec = {
diff --git a/tests/test_rpc.py b/tests/test_rpc.py
index e7b2283..a6e3f4f 100644
--- a/tests/test_rpc.py
+++ b/tests/test_rpc.py
@@ -19,6 +19,7 @@
 from thriftpy2.transport import TTransportException  # noqa
 from thriftpy2.thrift import TApplicationException  # noqa
 
+multiprocessing.set_start_method("fork", force=True)
 
 if sys.platform == "win32":
     pytest.skip("requires unix domain socket", allow_module_level=True)
diff --git a/tests/test_tracking.py b/tests/test_tracking.py
index 9d71d4d..602891c 100644
--- a/tests/test_tracking.py
+++ b/tests/test_tracking.py
@@ -58,6 +58,7 @@
 else:
     cleanup_on_sigterm()
 
+multiprocessing.set_start_method("fork", force=True)
 
 if sys.platform == "win32":
     pytest.skip("requires fork", allow_module_level=True)