diff --git a/duration.go b/duration.go
index 92d65f9..30ed6aa 100644
--- a/duration.go
+++ b/duration.go
@@ -1,3 +1,5 @@
+// @generated Code generated by gen-atomicwrapper.
+
 // Copyright (c) 2020 Uber Technologies, Inc.
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy
@@ -25,65 +27,56 @@
 	"time"
 )
 
-// Duration is an atomic wrapper around time.Duration
-// https://godoc.org/time#Duration
+// Duration is an atomic type-safe wrapper for time.Duration values.
 type Duration struct {
 	nocmp // disallow non-atomic comparison
 
 	v Int64
 }
 
-// NewDuration creates a Duration.
-func NewDuration(d time.Duration) *Duration {
-	return &Duration{v: *NewInt64(int64(d))}
+var _zeroDuration time.Duration
+
+// NewDuration creates a new Duration.
+func NewDuration(v time.Duration) *Duration {
+	x := &Duration{}
+	if v != _zeroDuration {
+		x.Store(v)
+	}
+	return x
 }
 
-// Load atomically loads the wrapped value.
-func (d *Duration) Load() time.Duration {
-	return time.Duration(d.v.Load())
+// Load atomically loads the wrapped time.Duration.
+func (x *Duration) Load() time.Duration {
+	return time.Duration(x.v.Load())
 }
 
-// Store atomically stores the passed value.
-func (d *Duration) Store(n time.Duration) {
-	d.v.Store(int64(n))
+// Store atomically stores the passed time.Duration.
+func (x *Duration) Store(v time.Duration) {
+	x.v.Store(int64(v))
 }
 
-// Add atomically adds to the wrapped time.Duration and returns the new value.
-func (d *Duration) Add(n time.Duration) time.Duration {
-	return time.Duration(d.v.Add(int64(n)))
+// CAS is an atomic compare-and-swap for time.Duration values.
+func (x *Duration) CAS(o, n time.Duration) bool {
+	return x.v.CAS(int64(o), int64(n))
 }
 
-// Sub atomically subtracts from the wrapped time.Duration and returns the new value.
-func (d *Duration) Sub(n time.Duration) time.Duration {
-	return time.Duration(d.v.Sub(int64(n)))
-}
-
-// Swap atomically swaps the wrapped time.Duration and returns the old value.
-func (d *Duration) Swap(n time.Duration) time.Duration {
-	return time.Duration(d.v.Swap(int64(n)))
-}
-
-// CAS is an atomic compare-and-swap.
-func (d *Duration) CAS(old, new time.Duration) bool {
-	return d.v.CAS(int64(old), int64(new))
+// Swap atomically stores the given time.Duration and returns the old
+// value.
+func (x *Duration) Swap(o time.Duration) time.Duration {
+	return time.Duration(x.v.Swap(int64(o)))
 }
 
 // MarshalJSON encodes the wrapped time.Duration into JSON.
-func (d *Duration) MarshalJSON() ([]byte, error) {
-	return json.Marshal(d.Load())
+func (x *Duration) MarshalJSON() ([]byte, error) {
+	return json.Marshal(x.Load())
 }
 
-// UnmarshalJSON decodes JSON into the wrapped time.Duration.
-func (d *Duration) UnmarshalJSON(b []byte) error {
+// UnmarshalJSON decodes a time.Duration from JSON.
+func (x *Duration) UnmarshalJSON(b []byte) error {
 	var v time.Duration
 	if err := json.Unmarshal(b, &v); err != nil {
 		return err
 	}
-	d.Store(v)
+	x.Store(v)
 	return nil
 }
-
-// String encodes the wrapped value as a string.
-func (d *Duration) String() string {
-	return d.Load().String()
-}
diff --git a/duration_ext.go b/duration_ext.go
new file mode 100644
index 0000000..6273b66
--- /dev/null
+++ b/duration_ext.go
@@ -0,0 +1,40 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package atomic
+
+import "time"
+
+//go:generate bin/gen-atomicwrapper -name=Duration -type=time.Duration -wrapped=Int64 -pack=int64 -unpack=time.Duration -cas -swap -json -imports time -file=duration.go
+
+// Add atomically adds to the wrapped time.Duration and returns the new value.
+func (d *Duration) Add(n time.Duration) time.Duration {
+	return time.Duration(d.v.Add(int64(n)))
+}
+
+// Sub atomically subtracts from the wrapped time.Duration and returns the new value.
+func (d *Duration) Sub(n time.Duration) time.Duration {
+	return time.Duration(d.v.Sub(int64(n)))
+}
+
+// String encodes the wrapped value as a string.
+func (d *Duration) String() string {
+	return d.Load().String()
+}