diff --git a/packer/rpc/muxconn.go b/packer/rpc/muxconn.go
index 8ff8b4aec..9201dfaa7 100644
--- a/packer/rpc/muxconn.go
+++ b/packer/rpc/muxconn.go
@@ -241,7 +241,9 @@ func (m *MuxConn) loop() {
 		m.mu.Lock()
 		defer m.mu.Unlock()
 		for _, w := range m.streams {
+			w.mu.Lock()
 			w.remoteClose()
+			w.mu.Unlock()
 		}
 	}()