diff --git a/rpc/types.go b/rpc/types.go
index ebe3883735..5d8a62ed69 100644
--- a/rpc/types.go
+++ b/rpc/types.go
@@ -23,6 +23,7 @@ import (
 	"math"
 	"math/big"
 	"reflect"
+	"strconv"
 	"strings"
 	"sync"
 
@@ -275,6 +276,17 @@ func (bn BlockNumber) Int64() int64 {
 	return (int64)(bn)
 }
 
+func (bn BlockNumber) String() string {
+	switch bn {
+	case PendingBlockNumber:
+		return "pending"
+	case LatestBlockNumber:
+		return "latest"
+	default:
+		return "0x" + strconv.FormatInt(int64(bn), 16)
+	}
+}
+
 // HexBytes JSON-encodes as hex with 0x prefix.
 type HexBytes []byte