diff --git a/jsonpb/jsonpb.go b/jsonpb/jsonpb.go
index d1f6f28..768564e 100644
--- a/jsonpb/jsonpb.go
+++ b/jsonpb/jsonpb.go
@@ -41,6 +41,7 @@
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"reflect"
@@ -125,6 +126,10 @@
 			out.write(x)
 			out.write(`s"`)
 			return out.err
+		case "Struct":
+			// Let marshalValue handle the `fields` map.
+			// TODO: pass the correct Properties if needed.
+			return m.marshalValue(out, &proto.Properties{}, s.Field(0), indent)
 		case "Timestamp":
 			// "RFC 3339, where generated output will always be Z-normalized
 			//  and uses 3, 6 or 9 fractional digits."
@@ -138,6 +143,17 @@
 			out.write(x)
 			out.write(`Z"`)
 			return out.err
+		case "Value":
+			// Value has a single oneof.
+			kind := s.Field(0)
+			if kind.IsNil() {
+				// "absence of any variant indicates an error"
+				return errors.New("nil Value")
+			}
+			// oneof -> *T -> T -> T.F
+			x := kind.Elem().Elem().Field(0)
+			// TODO: pass the correct Properties if needed.
+			return m.marshalValue(out, &proto.Properties{}, x, indent)
 		}
 	}
 
@@ -304,6 +320,19 @@
 		return out.err
 	}
 
+	// Handle well-known types.
+	// Most are handled up in marshalObject (because 99% are messages).
+	type wkt interface {
+		XXX_WellKnownType() string
+	}
+	if wkt, ok := v.Interface().(wkt); ok {
+		switch wkt.XXX_WellKnownType() {
+		case "NullValue":
+			out.write("null")
+			return out.err
+		}
+	}
+
 	// Handle enumerations.
 	if !m.EnumsAsInts && prop.Enum != "" {
 		// Unknown enum values will are stringified by the proto library as their