diff --git a/migen/bus/wishbone.py b/migen/bus/wishbone.py
index ee579fb1f..bca7fce48 100644
--- a/migen/bus/wishbone.py
+++ b/migen/bus/wishbone.py
@@ -44,9 +44,14 @@ class Arbiter:
 		s2m_names = [GetSigName(x, False) for x in _desc if not x[0]]
 		for name in s2m_names:
 			source = getattr(self.target, name)
+			i = 0
 			for m in self.masters:
 				dest = getattr(m, name)
-				comb.append(f.Assign(dest, source))
+				if name == "ack_i" or name == "err_i":
+					comb.append(f.Assign(dest, source & (self.rr.grant == f.Constant(i, self.rr.grant.bv))))
+				else:
+					comb.append(f.Assign(dest, source))
+				i += 1
 		
 		# connect bus requests to round-robin selector
 		reqs = [m.cyc_o for m in self.masters]
@@ -54,7 +59,6 @@ class Arbiter:
 		
 		return f.Fragment(comb) + self.rr.GetFragment()
 
-
 class Decoder:
 	# slaves is a list of pairs:
 	# 0) structure.Constant defining address (always decoded on the upper bits)