diff --git a/decor/decorator.go b/decor/decorator.go
index daa86fc..5bca63d 100644
--- a/decor/decorator.go
+++ b/decor/decorator.go
@@ -85,16 +85,16 @@
 }
 
 // EwmaDecorator interface.
-// EWMA based decorators must to implement this one.
+// EWMA based decorators should implement this one.
 type EwmaDecorator interface {
-	IterationUpdate(int64, time.Duration)
+	EwmaUpdate(int64, time.Duration)
 }
 
 // AverageDecorator interface.
 // Average decorators should implement this interface to provide start
 // time adjustment facility, for resume-able tasks.
 type AverageDecorator interface {
-	Adjust(time.Time)
+	AverageAdjust(time.Time)
 }
 
 // ShutdownListener interface.
diff --git a/decor/eta.go b/decor/eta.go
index 5955f1e..f0c97dd 100644
--- a/decor/eta.go
+++ b/decor/eta.go
@@ -27,12 +27,13 @@
 // work duration as second argument, in order for this decorator to
 // work correctly. This decorator is a wrapper of MovingAverageETA.
 func EwmaETA(style TimeStyle, age float64, wcc ...WC) Decorator {
-	var average MovingAverage
+	var average ewma.MovingAverage
 	if age == 0 {
 		average = ewma.NewMovingAverage()
 	} else {
 		average = ewma.NewMovingAverage(age)
 	}
+	average = &ThreadSafeMovingAverage{MovingAverage: average}
 	return MovingAverageETA(style, average, nil, wcc...)
 }
 
@@ -46,7 +47,7 @@
 //
 //	`wcc` optional WC config
 //
-func MovingAverageETA(style TimeStyle, average MovingAverage, normalizer TimeNormalizer, wcc ...WC) Decorator {
+func MovingAverageETA(style TimeStyle, average ewma.MovingAverage, normalizer TimeNormalizer, wcc ...WC) Decorator {
 	d := &movingAverageETA{
 		WC:         initWC(wcc...),
 		average:    average,
@@ -72,12 +73,8 @@
 	return d.FormatMsg(d.producer(remaining))
 }
 
-func (d *movingAverageETA) NextAmount(n int64, wdd ...time.Duration) {
-	var workDuration time.Duration
-	for _, wd := range wdd {
-		workDuration = wd
-	}
-	durPerItem := float64(workDuration) / float64(n)
+func (d *movingAverageETA) EwmaUpdate(n int64, dur time.Duration) {
+	durPerItem := float64(dur) / float64(n)
 	if math.IsInf(durPerItem, 0) || math.IsNaN(durPerItem) {
 		return
 	}
diff --git a/decor/moving_average.go b/decor/moving_average.go
index 933b1f2..5d2d3a0 100644
--- a/decor/moving_average.go
+++ b/decor/moving_average.go
@@ -2,14 +2,34 @@
 
 import (
 	"sort"
+	"sync"
 
 	"github.com/VividCortex/ewma"
 )
 
-// MovingAverage is the interface that computes a moving average over
-// a time-series stream of numbers. The average may be over a window
-// or exponentially decaying.
-type MovingAverage = ewma.MovingAverage
+// ThreadSafeMovingAverage is a thread safe wrapper for ewma.MovingAverage.
+type ThreadSafeMovingAverage struct {
+	ewma.MovingAverage
+	mu sync.Mutex
+}
+
+func (s *ThreadSafeMovingAverage) Add(value float64) {
+	s.mu.Lock()
+	s.MovingAverage.Add(value)
+	s.mu.Unlock()
+}
+
+func (s *ThreadSafeMovingAverage) Value() float64 {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.MovingAverage.Value()
+}
+
+func (s *ThreadSafeMovingAverage) Set(value float64) {
+	s.mu.Lock()
+	s.MovingAverage.Set(value)
+	s.mu.Unlock()
+}
 
 type medianWindow [3]float64
 
@@ -35,6 +55,6 @@
 }
 
 // NewMedian is fixed last 3 samples median MovingAverage.
-func NewMedian() MovingAverage {
-	return new(medianWindow)
+func NewMedian() ewma.MovingAverage {
+	return &ThreadSafeMovingAverage{MovingAverage: new(medianWindow)}
 }
diff --git a/decor/speed.go b/decor/speed.go
index 92d13e6..142e5be 100644
--- a/decor/speed.go
+++ b/decor/speed.go
@@ -32,12 +32,13 @@
 // work duration as second argument, in order for this decorator to
 // work correctly. This decorator is a wrapper of MovingAverageSpeed.
 func EwmaSpeed(unit int, format string, age float64, wcc ...WC) Decorator {
-	var average MovingAverage
+	var average ewma.MovingAverage
 	if age == 0 {
 		average = ewma.NewMovingAverage()
 	} else {
 		average = ewma.NewMovingAverage(age)
 	}
+	average = &ThreadSafeMovingAverage{MovingAverage: average}
 	return MovingAverageSpeed(unit, format, average, wcc...)
 }
 
@@ -59,7 +60,7 @@
 //	unit=UnitKB,  format="%.1f"  output: "1.0MB/s"
 //	unit=UnitKB,  format="% .1f" output: "1.0 MB/s"
 //
-func MovingAverageSpeed(unit int, format string, average MovingAverage, wcc ...WC) Decorator {
+func MovingAverageSpeed(unit int, format string, average ewma.MovingAverage, wcc ...WC) Decorator {
 	if format == "" {
 		format = "%.0f"
 	}
@@ -89,12 +90,8 @@
 	return d.FormatMsg(d.msg)
 }
 
-func (d *movingAverageSpeed) NextAmount(n int64, wdd ...time.Duration) {
-	var workDuration time.Duration
-	for _, wd := range wdd {
-		workDuration = wd
-	}
-	durPerByte := float64(workDuration) / float64(n)
+func (d *movingAverageSpeed) EwmaUpdate(n int64, dur time.Duration) {
+	durPerByte := float64(dur) / float64(n)
 	if math.IsInf(durPerByte, 0) || math.IsNaN(durPerByte) {
 		return
 	}