diff --git a/manual.go b/manual.go
index d5fdb9d..9e14787 100644
--- a/manual.go
+++ b/manual.go
@@ -1,35 +1,71 @@
 package progress
 
+import (
+	"sync"
+	"sync/atomic"
+)
+
 type Manual struct {
-	N     int64
-	Total int64
-	Err   error
+	n        int64
+	total    int64
+	err      error
+	errMutex sync.Mutex
+}
+
+func NewManual(size int64) *Manual {
+	return &Manual{
+		total: size,
+	}
 }
 
-func (p Manual) Current() int64 {
-	return int64(p.N)
+func (p *Manual) Current() int64 {
+	return atomic.LoadInt64(&p.n)
 }
 
-func (p Manual) Size() int64 {
-	return int64(p.Total)
+func (p *Manual) Size() int64 {
+	return atomic.LoadInt64(&p.total)
 }
 
-func (p Manual) Error() error {
-	return p.Err
+func (p *Manual) Error() error {
+	p.errMutex.Lock()
+	defer p.errMutex.Unlock()
+	return p.err
 }
 
-func (p Manual) Progress() Progress {
+func (p *Manual) SetError(err error) {
+	p.errMutex.Lock()
+	defer p.errMutex.Unlock()
+	p.err = err
+}
+
+func (p *Manual) Progress() Progress {
 	return Progress{
-		current: p.N,
-		size:    p.Total,
-		err:     p.Err,
+		current: p.Current(),
+		size:    p.Size(),
+		err:     p.Error(),
 	}
 }
 
+func (p *Manual) Add(n int64) {
+	atomic.AddInt64(&p.n, n)
+}
+
+func (p *Manual) Increment() {
+	atomic.AddInt64(&p.n, 1)
+}
+
+func (p *Manual) Set(n int64) {
+	atomic.StoreInt64(&p.n, n)
+}
+
+func (p *Manual) SetTotal(total int64) {
+	atomic.StoreInt64(&p.total, total)
+}
+
 func (p *Manual) SetCompleted() {
-	p.Err = ErrCompleted
-	if p.N > 0 && p.Total <= 0 {
-		p.Total = p.N
+	p.SetError(ErrCompleted)
+	if p.Current() > 0 && p.Size() <= 0 {
+		p.SetTotal(p.Current())
 		return
 	}
 }
diff --git a/reader.go b/reader.go
index 4b6c07a..f782662 100644
--- a/reader.go
+++ b/reader.go
@@ -8,31 +8,27 @@ import (
 
 // Reader should wrap another reader (acts as a bytes pass through)
 type Reader struct {
-	reader io.Reader
+	reader  io.Reader
 	monitor *Manual
 }
 
 func NewSizedReader(reader io.Reader, size int64) *Reader {
 	return &Reader{
-		reader: reader,
-		monitor: &Manual{
-			Total: size,
-		},
+		reader:  reader,
+		monitor: NewManual(size),
 	}
 }
 
 func NewReader(reader io.Reader) *Reader {
 	return &Reader{
-		reader: reader,
-		monitor: &Manual{
-			Total: -1,
-		},
+		reader:  reader,
+		monitor: NewManual(-1),
 	}
 }
 
 func NewProxyReader(reader io.Reader, monitor *Manual) *Reader {
 	return &Reader{
-		reader: reader,
+		reader:  reader,
 		monitor: monitor,
 	}
 }
@@ -42,26 +38,26 @@ func (r *Reader) SetReader(reader io.Reader) {
 }
 
 func (r *Reader) SetCompleted() {
-	r.monitor.Err = multierror.Append(r.monitor.Err, ErrCompleted)
+	r.monitor.SetError(multierror.Append(r.monitor.Error(), ErrCompleted))
 }
 
 func (r *Reader) Read(p []byte) (n int, err error) {
 	bytes, err := r.reader.Read(p)
-	r.monitor.N += int64(bytes)
+	r.monitor.Add(int64(bytes))
 	if err != nil {
-		r.monitor.Err = multierror.Append(r.monitor.Err, err)
+		r.monitor.SetError(multierror.Append(r.monitor.Error(), err))
 	}
 	return bytes, err
 }
 
 func (r *Reader) Current() int64 {
-	return r.monitor.N
+	return r.monitor.Current()
 }
 
 func (r *Reader) Size() int64 {
-	return r.monitor.Total
+	return r.monitor.Size()
 }
 
 func (r *Reader) Error() error {
-	return r.monitor.Err
+	return r.monitor.Error()
 }