diff --git a/pkg/runtime/serializer/protobuf/protobuf.go b/pkg/runtime/serializer/protobuf/protobuf.go
index b9eb9e5db86..a21df48a05d 100644
--- a/pkg/runtime/serializer/protobuf/protobuf.go
+++ b/pkg/runtime/serializer/protobuf/protobuf.go
@@ -124,7 +124,7 @@ func (s *Serializer) Decode(originalData []byte, gvk *unversioned.GroupVersionKi
 
 	if intoUnknown, ok := into.(*runtime.Unknown); ok && intoUnknown != nil {
 		*intoUnknown = unk
-		if len(intoUnknown.ContentType) == 0 {
+		if ok, _ := s.RecognizesData(bytes.NewBuffer(unk.Raw)); ok {
 			intoUnknown.ContentType = s.contentType
 		}
 		return intoUnknown, &actual, nil
@@ -167,17 +167,30 @@ func (s *Serializer) Decode(originalData []byte, gvk *unversioned.GroupVersionKi
 
 // Encode serializes the provided object to the given writer.
 func (s *Serializer) Encode(obj runtime.Object, w io.Writer) error {
-	var unk runtime.Unknown
-	kind := obj.GetObjectKind().GroupVersionKind()
-	unk = runtime.Unknown{
-		TypeMeta: runtime.TypeMeta{
-			Kind:       kind.Kind,
-			APIVersion: kind.GroupVersion().String(),
-		},
-	}
-
 	prefixSize := uint64(len(s.prefix))
 
+	var unk runtime.Unknown
+	switch t := obj.(type) {
+	case *runtime.Unknown:
+		estimatedSize := prefixSize + uint64(t.Size())
+		data := make([]byte, estimatedSize)
+		i, err := t.MarshalTo(data[prefixSize:])
+		if err != nil {
+			return err
+		}
+		copy(data, s.prefix)
+		_, err = w.Write(data[:prefixSize+uint64(i)])
+		return err
+	default:
+		kind := obj.GetObjectKind().GroupVersionKind()
+		unk = runtime.Unknown{
+			TypeMeta: runtime.TypeMeta{
+				Kind:       kind.Kind,
+				APIVersion: kind.GroupVersion().String(),
+			},
+		}
+	}
+
 	switch t := obj.(type) {
 	case bufferedMarshaller:
 		// this path performs a single allocation during write but requires the caller to implement
diff --git a/pkg/runtime/serializer/protobuf/protobuf_test.go b/pkg/runtime/serializer/protobuf/protobuf_test.go
index 54c92bf42a0..77a291da8ec 100644
--- a/pkg/runtime/serializer/protobuf/protobuf_test.go
+++ b/pkg/runtime/serializer/protobuf/protobuf_test.go
@@ -205,7 +205,7 @@ func TestDecode(t *testing.T) {
 		0x0a, 0x15,
 		0x0a, 0x0d, 0x6f, 0x74, 0x68, 0x65, 0x72, 0x2f, 0x76, 0x65, 0x72, 0x73, 0x69, 0x6f, 0x6e, // apiversion
 		0x12, 0x04, 0x74, 0x65, 0x73, 0x74, // kind
-		0x12, 0x03, 0x01, 0x02, 0x03, // data
+		0x12, 0x07, 0x6b, 0x38, 0x73, 0x00, 0x01, 0x02, 0x03, // data
 		0x1a, 0x00, // content-type
 		0x22, 0x00, // content-encoding
 	}
@@ -227,8 +227,7 @@ func TestDecode(t *testing.T) {
 		},
 		{
 			obj: &runtime.Unknown{
-				ContentType: "application/protobuf",
-				Raw:         []byte{},
+				Raw: []byte{},
 			},
 			data: wire1,
 		},
@@ -238,8 +237,9 @@ func TestDecode(t *testing.T) {
 					APIVersion: "other/version",
 					Kind:       "test",
 				},
+				// content type is set because the prefix matches the content
 				ContentType: "application/protobuf",
-				Raw:         []byte{0x01, 0x02, 0x03},
+				Raw:         []byte{0x6b, 0x38, 0x73, 0x00, 0x01, 0x02, 0x03},
 			},
 			data: wire2,
 		},