src/Pure/Tools/build.scala

--- a/src/Pure/Tools/build.scala	Sat Mar 18 20:57:15 2017 +0100
+++ b/src/Pure/Tools/build.scala	Sat Mar 18 21:24:54 2017 +0100
@@ -223,7 +223,7 @@
           val resources = new Resources(deps(parent))
           val session = new Session(options, resources)
           val handler = new Handler(progress, session, name)
-          session.add_protocol_handler(handler)
+          session.init_protocol_handler(handler)
 
           val session_result = Future.promise[Int]