diff --git a/decor/eta.go b/decor/eta.go
index 0df4024..1732fb7 100644
--- a/decor/eta.go
+++ b/decor/eta.go
@@ -81,6 +81,7 @@
 	return d.Format(d.producer(remaining))
 }
 
+// EwmaUpdate is called concurrently with (d *movingAverageETA).Decor
 func (d *movingAverageETA) EwmaUpdate(n int64, dur time.Duration) {
 	if n <= 0 {
 		d.zDur += dur
diff --git a/decor/speed.go b/decor/speed.go
index 9a6d573..808d6b6 100644
--- a/decor/speed.go
+++ b/decor/speed.go
@@ -93,6 +93,7 @@
 	return d.Format(str)
 }
 
+// EwmaUpdate is called concurrently with (d *movingAverageSpeed).Decor
 func (d *movingAverageSpeed) EwmaUpdate(n int64, dur time.Duration) {
 	if n <= 0 {
 		d.zDur += dur