diff --git a/call_opt_test.go b/call_opt_test.go
index 37dc556..b64f661 100644
--- a/call_opt_test.go
+++ b/call_opt_test.go
@@ -2,7 +2,6 @@ package jsonrpc2_test
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"testing"
 
@@ -108,18 +107,22 @@ func TestExtraField(t *testing.T) {
 				t.Error(err)
 			}
 		}
-		var sessionId *json.RawMessage
+		var sessionID string
 		for _, field := range req.ExtraFields {
 			if field.Name != "sessionId" {
 				continue
 			}
-			sessionId = field.Value
+			var ok bool
+			sessionID, ok = field.Value.(string)
+			if !ok {
+				t.Errorf("\"sessionId\" is not a string: %v", field.Value)
+			}
 		}
-		if sessionId == nil {
+		if sessionID == "" {
 			replyWithError("sessionId must be set")
 			return
 		}
-		if string(*sessionId) != `"session"` {
+		if sessionID != "session" {
 			replyWithError("sessionId has the wrong value")
 			return
 		}
diff --git a/jsonrpc2.go b/jsonrpc2.go
index 0fdb675..7e3bace 100644
--- a/jsonrpc2.go
+++ b/jsonrpc2.go
@@ -33,7 +33,7 @@ type JSONRPC2 interface {
 // RequestField is a top-level field that can be added to the JSON-RPC request.
 type RequestField struct {
 	Name  string
-	Value *json.RawMessage
+	Value interface{}
 }
 
 // Request represents a JSON-RPC request or
@@ -83,46 +83,64 @@ func (r Request) MarshalJSON() ([]byte, error) {
 
 // UnmarshalJSON implements json.Unmarshaler.
 func (r *Request) UnmarshalJSON(data []byte) error {
-	var r2 struct {
-		Method string           `json:"method"`
-		Params *json.RawMessage `json:"params,omitempty"`
-		Meta   *json.RawMessage `json:"meta,omitempty"`
-		ID     *ID              `json:"id"`
-	}
-	// This is used to get the extra fields, which are not type-safe.
-	r3 := make(map[string]*json.RawMessage)
+	r2 := make(map[string]interface{})
 
 	// Detect if the "params" field is JSON "null" or just not present
 	// by seeing if the field gets overwritten to nil.
-	r2.Params = &json.RawMessage{}
+	emptyParams := &json.RawMessage{}
+	r2["params"] = emptyParams
 
-	if err := json.Unmarshal(data, &r2); err != nil {
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.UseNumber()
+	if err := decoder.Decode(&r2); err != nil {
 		return err
 	}
-	if err := json.Unmarshal(data, &r3); err != nil {
-		return err
+	var ok bool
+	r.Method, ok = r2["method"].(string)
+	if !ok {
+		return errors.New("missing method field")
 	}
-	r.Method = r2.Method
 	switch {
-	case r2.Params == nil:
+	case r2["params"] == nil:
 		r.Params = &jsonNull
-	case len(*r2.Params) == 0:
+	case r2["params"] == emptyParams:
 		r.Params = nil
 	default:
-		r.Params = r2.Params
+		b, err := json.Marshal(r2["params"])
+		if err != nil {
+			return fmt.Errorf("failed to marshal params: %w", err)
+		}
+		r.Params = (*json.RawMessage)(&b)
 	}
-	r.Meta = r2.Meta
-	if r2.ID == nil {
+	meta, ok := r2["meta"]
+	if ok {
+		b, err := json.Marshal(meta)
+		if err != nil {
+			return fmt.Errorf("failed to marshal Meta: %w", err)
+		}
+		r.Meta = (*json.RawMessage)(&b)
+	}
+	switch rawID := r2["id"].(type) {
+	case nil:
 		r.ID = ID{}
 		r.Notif = true
-	} else {
-		r.ID = *r2.ID
+	case string:
+		r.ID = ID{Str: rawID, IsString: true}
 		r.Notif = false
+	case json.Number:
+		id, err := rawID.Int64()
+		if err != nil {
+			return fmt.Errorf("failed to unmarshal ID: %w", err)
+		}
+		r.ID = ID{Num: uint64(id)}
+		r.Notif = false
+	default:
+		return fmt.Errorf("unexpected ID type: %T", rawID)
 	}
 
 	// Clear the extra fields before populating them again.
 	r.ExtraFields = nil
-	for name, value := range r3 {
+	for name, value := range r2 {
 		switch name {
 		case "id", "jsonrpc", "meta", "method", "params":
 			continue
@@ -161,13 +179,9 @@ func (r *Request) SetMeta(v interface{}) error {
 // JSON representation of the request, as a way to add arbitrary extensions to
 // JSON RPC 2.0. If JSON marshaling fails, it returns an error.
 func (r *Request) SetExtraField(name string, v interface{}) error {
-	b, err := json.Marshal(v)
-	if err != nil {
-		return err
-	}
 	r.ExtraFields = append(r.ExtraFields, RequestField{
 		Name:  name,
-		Value: (*json.RawMessage)(&b),
+		Value: v,
 	})
 	return nil
 }
diff --git a/object_test.go b/object_test.go
index 686f4c9..cfa5b00 100644
--- a/object_test.go
+++ b/object_test.go
@@ -39,7 +39,6 @@ func TestAnyMessage(t *testing.T) {
 func TestRequest_MarshalUnmarshalJSON(t *testing.T) {
 	null := json.RawMessage("null")
 	obj := json.RawMessage(`{"foo":"bar"}`)
-	requestFieldValue := json.RawMessage(`"session"`)
 	tests := []struct {
 		data []byte
 		want Request
@@ -58,7 +57,7 @@ func TestRequest_MarshalUnmarshalJSON(t *testing.T) {
 		},
 		{
 			data: []byte(`{"id":123,"jsonrpc":"2.0","method":"m","sessionId":"session"}`),
-			want: Request{ID: ID{Num: 123}, Method: "m", Params: nil, ExtraFields: []RequestField{{Name: "sessionId", Value: &requestFieldValue}}},
+			want: Request{ID: ID{Num: 123}, Method: "m", Params: nil, ExtraFields: []RequestField{{Name: "sessionId", Value: "session"}}},
 		},
 	}
 	for _, test := range tests {