diff --git a/src/common/parser/EscapeSequenceParser.test.ts b/src/common/parser/EscapeSequenceParser.test.ts
index 6a1e20eff..a5d35de9b 100644
--- a/src/common/parser/EscapeSequenceParser.test.ts
+++ b/src/common/parser/EscapeSequenceParser.test.ts
@@ -3,14 +3,13 @@
  * @license MIT
  */
 
-import { IDcsHandler, IParsingState, IParams } from 'common/parser/Types';
+import { IDcsHandler, IParsingState, IParams, ParamsArray } from 'common/parser/Types';
 import { EscapeSequenceParser, TransitionTable, VT500_TRANSITION_TABLE } from 'common/parser/EscapeSequenceParser';
 import * as chai from 'chai';
 import { StringToUtf32, stringFromCodePoint } from 'common/input/TextDecoder';
 import { ParserState } from 'common/parser/Constants';
 import { Params } from 'common/parser/Params';
 
-type ParamsArray = (number | number[])[];
 
 function r(a: number, b: number): string[] {
   let c = b - a;
@@ -30,7 +29,7 @@ class TestEscapeSequenceParser extends EscapeSequenceParser {
     this._osc = value;
   }
   public get params(): ParamsArray {
-    return this._params.toArray() as ParamsArray;
+    return this._params.toArray();
   }
   public set params(value: ParamsArray) {
     this._params = Params.fromArray(value);
diff --git a/src/common/parser/Params.test.ts b/src/common/parser/Params.test.ts
index 3278287e8..01287b8f7 100644
--- a/src/common/parser/Params.test.ts
+++ b/src/common/parser/Params.test.ts
@@ -4,6 +4,7 @@
  */
 import { assert } from 'chai';
 import { Params } from 'common/parser/Params';
+import { ParamsArray } from 'common/parser/Types';
 
 class TestParams extends Params {
   public get subParams(): Int32Array {
@@ -108,7 +109,7 @@ describe('Params', () => {
     assert.deepEqual(params.toArray(), [1, [2, 3], 12345, [-1]]);
   });
   it('Params.fromArray --> toArray', () => {
-    let data: (number | number[])[] = [];
+    let data: ParamsArray = [];
     assert.deepEqual(Params.fromArray(data).toArray(), data);
     data = [1, [2, 3], 12345, [-1]];
     assert.deepEqual(Params.fromArray(data).toArray(), data);
diff --git a/src/common/parser/Params.ts b/src/common/parser/Params.ts
index 8a66a81aa..1ded5dcfc 100644
--- a/src/common/parser/Params.ts
+++ b/src/common/parser/Params.ts
@@ -2,7 +2,7 @@
  * Copyright (c) 2019 The xterm.js authors. All rights reserved.
  * @license MIT
  */
-import { IParams } from 'common/parser/Types';
+import { IParams, ParamsArray } from 'common/parser/Types';
 
 // max value supported for a single param/subparam (clamped to positive int32 range)
 const MAX_VALUE = 0x7FFFFFFF;
@@ -57,7 +57,7 @@ export class Params implements IParams {
   /**
    * Create a `Params` type from JS array representation.
    */
-  public static fromArray(values: (number | number[])[]): Params {
+  public static fromArray(values: ParamsArray): Params {
     const params = new Params();
     if (!values.length) {
       return params;
@@ -112,8 +112,8 @@ export class Params implements IParams {
    *    sequence: "1;2:3:4;5::6"
    *    array   : [1, 2, [3, 4], 5, [-1, 6]]
    */
-  public toArray(): (number | number[])[] {
-    const res: (number | number[])[] = [];
+  public toArray(): ParamsArray {
+    const res: ParamsArray = [];
     for (let i = 0; i < this.length; ++i) {
       res.push(this.params[i]);
       const start = this._subParamsIdx[i] >> 8;
diff --git a/src/common/parser/Types.d.ts b/src/common/parser/Types.d.ts
index 436c70af4..5f9256907 100644
--- a/src/common/parser/Types.d.ts
+++ b/src/common/parser/Types.d.ts
@@ -16,6 +16,8 @@ export interface IParamsConstructor {
   fromArray(values: (number | number[])[]): IParams;
 }
 
+export type ParamsArray = (number | number[])[];
+
 export interface IParams {
   /** from ctor */
   maxLength: number;
@@ -27,7 +29,7 @@ export interface IParams {
 
   /** methods */
   clone(): IParams;
-  toArray(): (number | number[])[];
+  toArray(): ParamsArray;
   reset(): void;
   addParam(value: number): void;
   addSubParam(value: number): void;