diff --git a/migen/actorlib/sim.py b/migen/actorlib/sim.py
index de11f1c..03d158d 100644
--- a/migen/actorlib/sim.py
+++ b/migen/actorlib/sim.py
@@ -30,13 +30,10 @@ class TokenExchanger(PureSimulable):
 				else:
 					s.wr(ep.ack, 1)
 			elif isinstance(ep, Source):
-				if s.rd(ep.stb):
-					if s.rd(ep.ack):
-						completed.add(token)
-						s.wr(ep.stb, 0)
-				else:
-					s.wr(ep.stb, 1)
-					s.multiwrite(ep.token, token.value)
+				if s.rd(ep.ack):
+					completed.add(token)
+				s.wr(ep.stb, 1)
+				s.multiwrite(ep.token, token.value)
 			else:
 				raise TypeError
 		self.active -= completed