diff --git a/waflib/Utils.py b/waflib/Utils.py
index 98f77632..a657ab36 100644
--- a/waflib/Utils.py
+++ b/waflib/Utils.py
@@ -821,6 +821,8 @@ def run_prefork_process(cmd, kwargs, cargs):
 	"""
 	Delegates process execution to a pre-forked process instance.
 	"""
+	if not 'env' in kwargs:
+		kwargs['env'] = os.environ
 	try:
 		obj = base64.b64encode(cPickle.dumps([cmd, kwargs, cargs]))
 	except TypeError: