diff --git a/utils/libcxx/test/config.py b/utils/libcxx/test/config.py
index 47784348d..fad9e8af1 100644
--- a/utils/libcxx/test/config.py
+++ b/utils/libcxx/test/config.py
@@ -67,7 +67,10 @@ class Configuration(object):
         self.abi_library_root = None
         self.link_shared = self.get_lit_bool('enable_shared', default=True)
         self.debug_build = self.get_lit_bool('debug_build',   default=False)
-        self.exec_env = {}
+        # FIXME: Some tests on Windows require we copy all of the environment
+        # variables into the runtime environment. Should we do this on other
+        # platforms too?
+        self.exec_env = {} if not self.is_windows else dict(os.environ)
         self.use_target = False
         self.use_system_cxx_lib = False
         self.use_clang_verify = False