diff --git a/jsonpb/jsonpb.go b/jsonpb/jsonpb.go
index 1f64aabb87..e8134ec8ba 100644
--- a/jsonpb/jsonpb.go
+++ b/jsonpb/jsonpb.go
@@ -164,6 +164,11 @@ type isWkt interface {
 	XXX_WellKnownType() string
 }
 
+var (
+	wktType     = reflect.TypeOf((*isWkt)(nil)).Elem()
+	messageType = reflect.TypeOf((*proto.Message)(nil)).Elem()
+)
+
 // marshalObject writes a struct to the Writer.
 func (m *Marshaler) marshalObject(out *errWriter, v proto.Message, indent, typeURL string) error {
 	if jsm, ok := v.(JSONPBMarshaler); ok {
@@ -551,7 +556,8 @@ func (m *Marshaler) marshalValue(out *errWriter, prop *proto.Properties, v refle
 
 	// Handle well-known types.
 	// Most are handled up in marshalObject (because 99% are messages).
-	if wkt, ok := v.Interface().(isWkt); ok {
+	if v.Type().Implements(wktType) {
+		wkt := v.Interface().(isWkt)
 		switch wkt.XXX_WellKnownType() {
 		case "NullValue":
 			out.write("null")
@@ -1422,8 +1428,8 @@ func checkRequiredFields(pb proto.Message) error {
 }
 
 func checkRequiredFieldsInValue(v reflect.Value) error {
-	if pm, ok := v.Interface().(proto.Message); ok {
-		return checkRequiredFields(pm)
+	if v.Type().Implements(messageType) {
+		return checkRequiredFields(v.Interface().(proto.Message))
 	}
 	return nil
 }
diff --git a/proto/all_test.go b/proto/all_test.go
index f391af74c3..966ceb567d 100644
--- a/proto/all_test.go
+++ b/proto/all_test.go
@@ -45,9 +45,11 @@ import (
 	"testing"
 	"time"
 
+	"github.com/gogo/protobuf/jsonpb"
 	. "github.com/gogo/protobuf/proto"
 	pb3 "github.com/gogo/protobuf/proto/proto3_proto"
 	. "github.com/gogo/protobuf/proto/test_proto"
+	descriptorpb "github.com/gogo/protobuf/protoc-gen-gogo/descriptor"
 )
 
 var globalO *Buffer
@@ -2509,3 +2511,33 @@ func BenchmarkUnmarshalUnrecognizedFields(b *testing.B) {
 		p2.Unmarshal(pbd)
 	}
 }
+
+// TestRace tests whether there are races among the different marshalers.
+func TestRace(t *testing.T) {
+	m := &descriptorpb.FileDescriptorProto{
+		Options: &descriptorpb.FileOptions{
+			GoPackage: String("path/to/my/package"),
+		},
+	}
+
+	wg := &sync.WaitGroup{}
+	defer wg.Wait()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		Marshal(m)
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		(&jsonpb.Marshaler{}).MarshalToString(m)
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		_ = m.String()
+	}()
+}
diff --git a/proto/text.go b/proto/text.go
index 0407ba85d0..87416afe95 100644
--- a/proto/text.go
+++ b/proto/text.go
@@ -476,6 +476,8 @@ func (tm *TextMarshaler) writeStruct(w *textWriter, sv reflect.Value) error {
 	return nil
 }
 
+var textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
+
 // writeAny writes an arbitrary field.
 func (tm *TextMarshaler) writeAny(w *textWriter, v reflect.Value, props *Properties) error {
 	v = reflect.Indirect(v)
@@ -589,8 +591,8 @@ func (tm *TextMarshaler) writeAny(w *textWriter, v reflect.Value, props *Propert
 			// mutating this value.
 			v = v.Addr()
 		}
-		if etm, ok := v.Interface().(encoding.TextMarshaler); ok {
-			text, err := etm.MarshalText()
+		if v.Type().Implements(textMarshalerType) {
+			text, err := v.Interface().(encoding.TextMarshaler).MarshalText()
 			if err != nil {
 				return err
 			}