diff --git a/Lib/wsgiref/simple_server.py b/Lib/wsgiref/simple_server.py
index f71563a..93d01a8 100644
--- a/Lib/wsgiref/simple_server.py
+++ b/Lib/wsgiref/simple_server.py
@@ -127,7 +127,8 @@
             return
 
         handler = ServerHandler(
-            self.rfile, self.wfile, self.get_stderr(), self.get_environ()
+            self.rfile, self.wfile, self.get_stderr(), self.get_environ(),
+            multithread=False,
         )
         handler.request_handler = self      # backpointer for logging
         handler.run(self.server.get_app())