diff --git a/bson/decode.go b/bson/decode.go
index 7c2d8416a..cf564385f 100644
--- a/bson/decode.go
+++ b/bson/decode.go
@@ -538,7 +538,12 @@ func (d *decoder) readElemTo(out reflect.Value, kind byte) (good bool) {
 	case 0x11: // Mongo-specific timestamp
 		in = MongoTimestamp(d.readInt64())
 	case 0x12: // Int64
-		in = d.readInt64()
+		switch out.Type() {
+		case typeTimeDuration:
+			in = time.Duration(time.Duration(d.readInt64()) * time.Millisecond)
+		default:
+			in = d.readInt64()
+		}
 	case 0x13: // Decimal128
 		in = Decimal128{
 			l: uint64(d.readInt64()),
diff --git a/bson/encode.go b/bson/encode.go
index add39e865..08f60df0b 100644
--- a/bson/encode.go
+++ b/bson/encode.go
@@ -54,6 +54,7 @@ var (
 	typeTime           = reflect.TypeOf(time.Time{})
 	typeString         = reflect.TypeOf("")
 	typeJSONNumber     = reflect.TypeOf(json.Number(""))
+	typeTimeDuration   = reflect.TypeOf(time.Duration(0))
 )
 
 const itoaCacheSize = 32
@@ -325,7 +326,11 @@ func (e *encoder) addElem(name string, v reflect.Value, minSize bool) {
 			} else {
 				e.addElemName(0xFF, name)
 			}
+		case typeTimeDuration:
+			// Stored as int64
+			e.addElemName(0x12, name)
 
+			e.addInt64(int64(v.Int()/1e6))
 		default:
 			i := v.Int()
 			if (minSize || v.Type().Kind() != reflect.Int64) && i >= math.MinInt32 && i <= math.MaxInt32 {