diff --git a/jsonpb/jsonpb.go b/jsonpb/jsonpb.go
index 82c6162..1fc8ae8 100644
--- a/jsonpb/jsonpb.go
+++ b/jsonpb/jsonpb.go
@@ -585,14 +585,7 @@
 		case "Any":
 			return fmt.Errorf("unmarshaling Any not supported yet")
 		case "Duration":
-			ivStr := string(inputValue)
-			if ivStr == "null" {
-				target.Field(0).SetInt(0)
-				target.Field(1).SetInt(0)
-				return nil
-			}
-
-			unq, err := strconv.Unquote(ivStr)
+			unq, err := strconv.Unquote(string(inputValue))
 			if err != nil {
 				return err
 			}
@@ -607,14 +600,7 @@
 			target.Field(1).SetInt(ns)
 			return nil
 		case "Timestamp":
-			ivStr := string(inputValue)
-			if ivStr == "null" {
-				target.Field(0).SetInt(0)
-				target.Field(1).SetInt(0)
-				return nil
-			}
-
-			unq, err := strconv.Unquote(ivStr)
+			unq, err := strconv.Unquote(string(inputValue))
 			if err != nil {
 				return err
 			}
diff --git a/jsonpb/jsonpb_test.go b/jsonpb/jsonpb_test.go
index e237df5..78f67c4 100644
--- a/jsonpb/jsonpb_test.go
+++ b/jsonpb/jsonpb_test.go
@@ -467,11 +467,9 @@
 	{"camelName input", Unmarshaler{}, `{"oBool":true}`, &pb.Simple{OBool: proto.Bool(true)}},
 
 	{"Duration", Unmarshaler{}, `{"dur":"3.000s"}`, &pb.KnownTypes{Dur: &durpb.Duration{Seconds: 3}}},
-	{"null Duration", Unmarshaler{}, `{"dur":null}`, &pb.KnownTypes{Dur: &durpb.Duration{Seconds: 0}}},
 	{"Timestamp", Unmarshaler{}, `{"ts":"2014-05-13T16:53:20.021Z"}`, &pb.KnownTypes{Ts: &tspb.Timestamp{Seconds: 14e8, Nanos: 21e6}}},
 	{"PreEpochTimestamp", Unmarshaler{}, `{"ts":"1969-12-31T23:59:58.999999995Z"}`, &pb.KnownTypes{Ts: &tspb.Timestamp{Seconds: -2, Nanos: 999999995}}},
 	{"ZeroTimeTimestamp", Unmarshaler{}, `{"ts":"0001-01-01T00:00:00Z"}`, &pb.KnownTypes{Ts: &tspb.Timestamp{Seconds: -62135596800, Nanos: 0}}},
-	{"null Timestamp", Unmarshaler{}, `{"ts":null}`, &pb.KnownTypes{Ts: &tspb.Timestamp{Seconds: 0, Nanos: 0}}},
 
 	{"DoubleValue", Unmarshaler{}, `{"dbl":1.2}`, &pb.KnownTypes{Dbl: &wpb.DoubleValue{Value: 1.2}}},
 	{"FloatValue", Unmarshaler{}, `{"flt":1.2}`, &pb.KnownTypes{Flt: &wpb.FloatValue{Value: 1.2}}},
diff --git a/proto/encode.go b/proto/encode.go
index 68b9b30..2b30f84 100644
--- a/proto/encode.go
+++ b/proto/encode.go
@@ -1075,10 +1075,17 @@
 
 func (o *Buffer) enc_exts(p *Properties, base structPointer) error {
 	exts := structPointer_Extensions(base, p.field)
-	if err := encodeExtensions(exts); err != nil {
+
+	v, mu := exts.extensionsRead()
+	if v == nil {
+		return nil
+	}
+
+	mu.Lock()
+	defer mu.Unlock()
+	if err := encodeExtensionsMap(v); err != nil {
 		return err
 	}
-	v, _ := exts.extensionsRead()
 
 	return o.enc_map_body(v)
 }
diff --git a/proto/extensions_test.go b/proto/extensions_test.go
index 403d7c6..b6d9114 100644
--- a/proto/extensions_test.go
+++ b/proto/extensions_test.go
@@ -40,6 +40,7 @@
 
 	"github.com/golang/protobuf/proto"
 	pb "github.com/golang/protobuf/proto/testdata"
+	"golang.org/x/sync/errgroup"
 )
 
 func TestGetExtensionsWithMissingExtensions(t *testing.T) {
@@ -506,3 +507,30 @@
 		t.Errorf("proto.HasExtension(%s): got true, want false", proto.MarshalTextString(m))
 	}
 }
+
+func TestMarshalRace(t *testing.T) {
+	// unregistered extension
+	desc := &proto.ExtensionDesc{
+		ExtendedType:  (*pb.MyMessage)(nil),
+		ExtensionType: (*bool)(nil),
+		Field:         101010100,
+		Name:          "emptyextension",
+		Tag:           "varint,0,opt",
+	}
+
+	m := &pb.MyMessage{Count: proto.Int32(4)}
+	if err := proto.SetExtension(m, desc, proto.Bool(true)); err != nil {
+		t.Errorf("proto.SetExtension(m, desc, true): got error %q, want nil", err)
+	}
+
+	var g errgroup.Group
+	for n := 3; n > 0; n-- {
+		g.Go(func() error {
+			_, err := proto.Marshal(m)
+			return err
+		})
+	}
+	if err := g.Wait(); err != nil {
+		t.Fatal(err)
+	}
+}