diff --git a/addons/xterm-addon-webgl/src/GlyphRenderer.ts b/addons/xterm-addon-webgl/src/GlyphRenderer.ts
index 4ae01698..186cb2c1 100644
--- a/addons/xterm-addon-webgl/src/GlyphRenderer.ts
+++ b/addons/xterm-addon-webgl/src/GlyphRenderer.ts
@@ -75,7 +75,7 @@ const BYTES_PER_CELL = INDICES_PER_CELL * Float32Array.BYTES_PER_ELEMENT;
 const CELL_POSITION_INDICES = 2;
 
 export class GlyphRenderer {
-  private _atlas: WebglCharAtlas;
+  private _atlas: WebglCharAtlas | undefined;
 
   private _program: WebGLProgram;
   private _vertexArrayObject: IWebGLVertexArrayObject;
@@ -188,6 +188,9 @@ export class GlyphRenderer {
     }
 
     let rasterizedGlyph: IRasterizedGlyph;
+    if (!this._atlas) {
+      throw new Error('atlas must be set before updating cell');
+    }
     if (chars && chars.length > 1) {
       rasterizedGlyph = this._atlas.getRasterizedGlyphCombinedChar(chars, attr, bg, fg);
     } else {
diff --git a/addons/xterm-addon-webgl/src/RectangleRenderer.ts b/addons/xterm-addon-webgl/src/RectangleRenderer.ts
index 3d755c98..2c464d2a 100644
--- a/addons/xterm-addon-webgl/src/RectangleRenderer.ts
+++ b/addons/xterm-addon-webgl/src/RectangleRenderer.ts
@@ -66,8 +66,8 @@ export class RectangleRenderer {
   private _resolutionLocation: WebGLUniformLocation;
   private _attributesBuffer: WebGLBuffer;
   private _projectionLocation: WebGLUniformLocation;
-  private _bgFloat: Float32Array;
-  private _selectionFloat: Float32Array;
+  private _bgFloat!: Float32Array;
+  private _selectionFloat!: Float32Array;
 
   private _vertices: IVertices = {
     count: 0,
diff --git a/addons/xterm-addon-webgl/src/WebglRenderer.ts b/addons/xterm-addon-webgl/src/WebglRenderer.ts
index 93befcec..3d41e1b5 100644
--- a/addons/xterm-addon-webgl/src/WebglRenderer.ts
+++ b/addons/xterm-addon-webgl/src/WebglRenderer.ts
@@ -27,7 +27,7 @@ export const INDICIES_PER_CELL = 4;
 
 export class WebglRenderer extends Disposable implements IRenderer {
   private _renderLayers: IRenderLayer[];
-  private _charAtlas: WebglCharAtlas;
+  private _charAtlas: WebglCharAtlas | undefined;
   private _devicePixelRatio: number;
 
   private _model: RenderModel = new RenderModel();
diff --git a/addons/xterm-addon-webgl/src/renderLayer/BaseRenderLayer.ts b/addons/xterm-addon-webgl/src/renderLayer/BaseRenderLayer.ts
index 5385e658..df0cdbab 100644
--- a/addons/xterm-addon-webgl/src/renderLayer/BaseRenderLayer.ts
+++ b/addons/xterm-addon-webgl/src/renderLayer/BaseRenderLayer.ts
@@ -19,7 +19,7 @@ import { throwIfFalsy } from '../WebglUtils';
 
 export abstract class BaseRenderLayer implements IRenderLayer {
   private _canvas: HTMLCanvasElement;
-  protected _ctx: CanvasRenderingContext2D;
+  protected _ctx!: CanvasRenderingContext2D;
   private _scaledCharWidth: number = 0;
   private _scaledCharHeight: number = 0;
   private _scaledCellWidth: number = 0;
@@ -27,7 +27,7 @@ export abstract class BaseRenderLayer implements IRenderLayer {
   private _scaledCharLeft: number = 0;
   private _scaledCharTop: number = 0;
 
-  protected _charAtlas: WebglCharAtlas;
+  protected _charAtlas: WebglCharAtlas | undefined;
 
   /**
    * An object that's reused when drawing glyphs in order to reduce GC.
diff --git a/addons/xterm-addon-webgl/src/renderLayer/CursorRenderLayer.ts b/addons/xterm-addon-webgl/src/renderLayer/CursorRenderLayer.ts
index d0a6aa82..6aed5f53 100644
--- a/addons/xterm-addon-webgl/src/renderLayer/CursorRenderLayer.ts
+++ b/addons/xterm-addon-webgl/src/renderLayer/CursorRenderLayer.ts
@@ -26,7 +26,7 @@ const BLINK_INTERVAL = 600;
 export class CursorRenderLayer extends BaseRenderLayer {
   private _state: ICursorState;
   private _cursorRenderers: {[key: string]: (terminal: Terminal, x: number, y: number, cell: ICellData) => void};
-  private _cursorBlinkStateManager: CursorBlinkStateManager;
+  private _cursorBlinkStateManager: CursorBlinkStateManager | undefined;
   private _cell: ICellData = new CellData();
 
   constructor(container: HTMLElement, zIndex: number, colors: IColorSet) {
diff --git a/addons/xterm-addon-webgl/src/tsconfig.json b/addons/xterm-addon-webgl/src/tsconfig.json
index 7e53b20d..00134015 100644
--- a/addons/xterm-addon-webgl/src/tsconfig.json
+++ b/addons/xterm-addon-webgl/src/tsconfig.json
@@ -15,7 +15,7 @@
       "common/*": [ "../../../src/common/*" ],
       "browser/*": [ "../../../src/browser/*" ]
     },
-    "strictNullChecks": true
+    "strict": true
   },
   "include": [
     "./**/*",