diff --git a/bar.go b/bar.go
index 9d114cd..30a3cea 100644
--- a/bar.go
+++ b/bar.go
@@ -448,12 +448,12 @@
 	}
 }
 
-func (b *Bar) forceRefresh(refreshCh chan interface{}) {
+func (b *Bar) forceRefresh(refreshCh chan<- interface{}) {
 	b.container.bwg.Add(1)
 	go b.forceRefreshImpl(refreshCh)
 }
 
-func (b *Bar) forceRefreshImpl(refreshCh chan interface{}) {
+func (b *Bar) forceRefreshImpl(refreshCh chan<- interface{}) {
 	defer b.container.bwg.Done()
 	var anyOtherRunning bool
 	b.container.traverseBars(func(bar *Bar) bool {
diff --git a/heap_manager.go b/heap_manager.go
index 079c0d0..757d5a5 100644
--- a/heap_manager.go
+++ b/heap_manager.go
@@ -24,7 +24,7 @@
 }
 
 type iterData struct {
-	iter chan *Bar
+	iter chan<- *Bar
 	drop chan struct{}
 }
 
@@ -111,12 +111,12 @@
 	m <- heapRequest{cmd: h_push, data: data}
 }
 
-func (m heapManager) iter(iter chan *Bar, drop chan struct{}) {
+func (m heapManager) iter(iter chan<- *Bar, drop chan struct{}) {
 	data := iterData{iter, drop}
 	m <- heapRequest{cmd: h_iter, data: data}
 }
 
-func (m heapManager) drain(iter chan *Bar, drop chan struct{}) {
+func (m heapManager) drain(iter chan<- *Bar, drop chan struct{}) {
 	data := iterData{iter, drop}
 	m <- heapRequest{cmd: h_drain, data: data}
 }