diff --git a/rpc/args.go b/rpc/args.go
index d31773ff7..9f99456e6 100644
--- a/rpc/args.go
+++ b/rpc/args.go
@@ -145,12 +145,8 @@ func (args *GetBlockByNumberArgs) UnmarshalJSON(b []byte) (err error) {
 		return NewInsufficientParamsError(len(obj), 2)
 	}
 
-	if v, ok := obj[0].(float64); ok {
-		args.BlockNumber = int64(v)
-	} else if v, ok := obj[0].(string); ok {
-		args.BlockNumber = common.Big(v).Int64()
-	} else {
-		return NewInvalidTypeError("blockNumber", "not a number or string")
+	if err := blockHeight(obj[0], &args.BlockNumber); err != nil {
+		return err
 	}
 
 	args.IncludeTxs = obj[1].(bool)
diff --git a/rpc/args_test.go b/rpc/args_test.go
index cfe6c0c45..e78981a41 100644
--- a/rpc/args_test.go
+++ b/rpc/args_test.go
@@ -355,6 +355,25 @@ func TestGetBlockByNumberArgsBlockHex(t *testing.T) {
 		t.Errorf("IncludeTxs should be %v but is %v", expected.IncludeTxs, args.IncludeTxs)
 	}
 }
+func TestGetBlockByNumberArgsWords(t *testing.T) {
+	input := `["earliest", true]`
+	expected := new(GetBlockByNumberArgs)
+	expected.BlockNumber = 0
+	expected.IncludeTxs = true
+
+	args := new(GetBlockByNumberArgs)
+	if err := json.Unmarshal([]byte(input), &args); err != nil {
+		t.Error(err)
+	}
+
+	if args.BlockNumber != expected.BlockNumber {
+		t.Errorf("BlockNumber should be %v but is %v", expected.BlockNumber, args.BlockNumber)
+	}
+
+	if args.IncludeTxs != expected.IncludeTxs {
+		t.Errorf("IncludeTxs should be %v but is %v", expected.IncludeTxs, args.IncludeTxs)
+	}
+}
 
 func TestGetBlockByNumberEmpty(t *testing.T) {
 	input := `[]`