diff --git a/addons/xterm-addon-canvas/src/CanvasAddon.ts b/addons/xterm-addon-canvas/src/CanvasAddon.ts
index dcd35704..1dc607e5 100644
--- a/addons/xterm-addon-canvas/src/CanvasAddon.ts
+++ b/addons/xterm-addon-canvas/src/CanvasAddon.ts
@@ -25,9 +25,7 @@ export class CanvasAddon extends Disposable implements ITerminalAddon {
   public activate(terminal: Terminal): void {
     const core = (terminal as any)._core;
     if (!terminal.element) {
-      this.register(toDisposable(() => {
-        core.onWillOpen(() => this.activate(terminal));
-      }));
+      this.register(core.onWillOpen(() => this.activate(terminal)));
       return;
     }
 
diff --git a/addons/xterm-addon-webgl/src/WebglAddon.ts b/addons/xterm-addon-webgl/src/WebglAddon.ts
index 538713c2..71487315 100644
--- a/addons/xterm-addon-webgl/src/WebglAddon.ts
+++ b/addons/xterm-addon-webgl/src/WebglAddon.ts
@@ -33,9 +33,7 @@ export class WebglAddon extends Disposable implements ITerminalAddon {
     }
     const core = (terminal as any)._core;
     if (!terminal.element) {
-      this.register(toDisposable(() => {
-        core.onWillOpen(() => this.activate(terminal));
-      }));
+      this.register(core.onWillOpen(() => this.activate(terminal)));
       return;
     }
     this._terminal = terminal;
diff --git a/addons/xterm-addon-webgl/src/WebglRenderer.ts b/addons/xterm-addon-webgl/src/WebglRenderer.ts
index ed99a225..8f747c03 100644
--- a/addons/xterm-addon-webgl/src/WebglRenderer.ts
+++ b/addons/xterm-addon-webgl/src/WebglRenderer.ts
@@ -103,6 +103,9 @@ export class WebglRenderer extends Disposable implements IRenderer {
       throw new Error('WebGL2 not supported ' + this._gl);
     }
 
+    // TODO: Remove me.
+    throw new Error('WebGL2 not supported ' + this._gl);
+
     this.register(addDisposableDomListener(this._canvas, 'webglcontextlost', (e) => {
       console.log('webglcontextlost event received');
       // Prevent the default behavior in order to enable WebGL context restoration.
diff --git a/demo/client.ts b/demo/client.ts
index 3228bd7f..6d48b302 100644
--- a/demo/client.ts
+++ b/demo/client.ts
@@ -61,26 +61,26 @@ interface IDemoAddon<T extends AddonType> {
   canChange: boolean;
   ctor: (
     T extends 'attach' ? typeof AttachAddon :
-      T extends 'canvas' ? typeof CanvasAddon :
-        T extends 'fit' ? typeof FitAddon :
-          T extends 'search' ? typeof SearchAddon :
-            T extends 'serialize' ? typeof SerializeAddon :
-              T extends 'web-links' ? typeof WebLinksAddon :
-                T extends 'unicode11' ? typeof Unicode11Addon :
-                  T extends 'ligatures' ? typeof LigaturesAddon :
-                    typeof WebglAddon
+    T extends 'canvas' ? typeof CanvasAddon :
+    T extends 'fit' ? typeof FitAddon :
+    T extends 'search' ? typeof SearchAddon :
+    T extends 'serialize' ? typeof SerializeAddon :
+    T extends 'web-links' ? typeof WebLinksAddon :
+    T extends 'unicode11' ? typeof Unicode11Addon :
+    T extends 'ligatures' ? typeof LigaturesAddon :
+    typeof WebglAddon
   );
   instance?: (
     T extends 'attach' ? AttachAddon :
-      T extends 'canvas' ? CanvasAddon :
-        T extends 'fit' ? FitAddon :
-          T extends 'search' ? SearchAddon :
-            T extends 'serialize' ? SerializeAddon :
-              T extends 'web-links' ? WebLinksAddon :
-                T extends 'webgl' ? WebglAddon :
-                  T extends 'unicode11' ? typeof Unicode11Addon :
-                    T extends 'ligatures' ? typeof LigaturesAddon :
-                      never
+    T extends 'canvas' ? CanvasAddon :
+    T extends 'fit' ? FitAddon :
+    T extends 'search' ? SearchAddon :
+    T extends 'serialize' ? SerializeAddon :
+    T extends 'web-links' ? WebLinksAddon :
+    T extends 'webgl' ? WebglAddon :
+    T extends 'unicode11' ? typeof Unicode11Addon :
+    T extends 'ligatures' ? typeof LigaturesAddon :
+    never
   );
 }
 
@@ -271,18 +271,20 @@ function createTerminal(): void {
   socketURL = protocol + location.hostname + ((location.port) ? (':' + location.port) : '') + '/terminals/';
 
   addons.fit.instance!.fit();
-  try { // try-catch to allow the demo to load if webgl is not supported
-    typedTerm.loadAddon(addons.webgl.instance);
-    setTimeout(() => {
+  typedTerm.loadAddon(addons.webgl.instance);
+  setTimeout(() => {
+    if (addons.webgl.instance !== undefined) {
       addTextureAtlas(addons.webgl.instance.textureAtlas);
       addons.webgl.instance.onChangeTextureAtlas(e => addTextureAtlas(e));
-    }, 0);
+    }
+  }, 0);
+
+  try { // try-catch to allow the demo to load if webgl is not supported
+    term.open(terminalContainer);
   }
   catch {
     addons.webgl.instance = undefined;
   }
-
-  term.open(terminalContainer);
   term.focus();
 
   addDomListener(paddingElement, 'change', setPadding);