diff --git a/src/runtime/chan.go b/src/runtime/chan.go
index 063c5ce391..f6f3ce4d90 100644
--- a/src/runtime/chan.go
+++ b/src/runtime/chan.go
@@ -203,6 +203,8 @@ func chansend(t *chantype, c *hchan, ep unsafe.Pointer, block bool, callerpc uin
 	if t0 != 0 {
 		mysg.releasetime = -1
 	}
+	// No stack splits between assigning elem and enqueuing mysg
+	// on gp.waiting where copystack can find it.
 	mysg.elem = ep
 	mysg.waitlink = nil
 	mysg.g = gp
@@ -460,6 +462,8 @@ func chanrecv(t *chantype, c *hchan, ep unsafe.Pointer, block bool) (selected, r
 	if t0 != 0 {
 		mysg.releasetime = -1
 	}
+	// No stack splits between assigning elem and enqueuing mysg
+	// on gp.waiting where copystack can find it.
 	mysg.elem = ep
 	mysg.waitlink = nil
 	gp.waiting = mysg
diff --git a/src/runtime/select.go b/src/runtime/select.go
index b6c3fea001..b315dde6c6 100644
--- a/src/runtime/select.go
+++ b/src/runtime/select.go
@@ -370,6 +370,8 @@ loop:
 		sg.g = gp
 		// Note: selectdone is adjusted for stack copies in stack1.go:adjustsudogs
 		sg.selectdone = (*uint32)(noescape(unsafe.Pointer(&done)))
+		// No stack splits between assigning elem and enqueuing
+		// sg on gp.waiting where copystack can find it.
 		sg.elem = cas.elem
 		sg.releasetime = 0
 		if t0 != 0 {