diff --git a/rpc/types.go b/rpc/types.go
index e7f0107ce5..04d1214e16 100644
--- a/rpc/types.go
+++ b/rpc/types.go
@@ -235,6 +235,16 @@ func (bnh *BlockNumberOrHash) Number() (BlockNumber, bool) {
 	return BlockNumber(0), false
 }
 
+func (bnh *BlockNumberOrHash) String() string {
+	if bnh.BlockNumber != nil {
+		return bnh.BlockNumber.String()
+	}
+	if bnh.BlockHash != nil {
+		return bnh.BlockHash.String()
+	}
+	return "nil"
+}
+
 func (bnh *BlockNumberOrHash) Hash() (common.Hash, bool) {
 	if bnh.BlockHash != nil {
 		return *bnh.BlockHash, true
diff --git a/rpc/types_test.go b/rpc/types_test.go
index f2019c43e7..861fe01165 100644
--- a/rpc/types_test.go
+++ b/rpc/types_test.go
@@ -155,3 +155,24 @@ func TestBlockNumberOrHash_WithNumber_MarshalAndUnmarshal(t *testing.T) {
 		})
 	}
 }
+
+func TestBlockNumberOrHash_StringAndUnmarshal(t *testing.T) {
+	tests := []BlockNumberOrHash{
+		BlockNumberOrHashWithNumber(math.MaxInt64),
+		BlockNumberOrHashWithNumber(PendingBlockNumber),
+		BlockNumberOrHashWithNumber(LatestBlockNumber),
+		BlockNumberOrHashWithNumber(EarliestBlockNumber),
+		BlockNumberOrHashWithNumber(32),
+		BlockNumberOrHashWithHash(common.Hash{0xaa}, false),
+	}
+	for _, want := range tests {
+		marshalled, _ := json.Marshal(want.String())
+		var have BlockNumberOrHash
+		if err := json.Unmarshal(marshalled, &have); err != nil {
+			t.Fatalf("cannot unmarshal (%v): %v", string(marshalled), err)
+		}
+		if !reflect.DeepEqual(want, have) {
+			t.Fatalf("wrong result: have %v, want %v", have, want)
+		}
+	}
+}