diff --git a/src/dispatch/shared-dispatch.js b/src/dispatch/shared-dispatch.js
index 85d38bde2..1e4785bce 100644
--- a/src/dispatch/shared-dispatch.js
+++ b/src/dispatch/shared-dispatch.js
@@ -91,6 +91,16 @@ class SharedDispatch {
         }
     }
 
+    /**
+     * Check if a particular service lives on another worker.
+     * @param {string} service - the service to check.
+     * @returns {boolean} - true if the service is remote (calls must cross a Worker boundary), false otherwise.
+     * @private
+     */
+    _isRemoteService (service) {
+        return this._getServiceProvider(service).isRemote;
+    }
+
     /**
      * Like {@link call}, but force the call to be posted through a particular communication channel.
      * @param {object} provider - send the call through this object's `postMessage` function.
diff --git a/src/extension-support/extension-manager.js b/src/extension-support/extension-manager.js
index d5a3e07ea..bdbc274f1 100644
--- a/src/extension-support/extension-manager.js
+++ b/src/extension-support/extension-manager.js
@@ -198,7 +198,17 @@ class ExtensionManager {
         blockInfo.opcode = this._sanitizeID(blockInfo.opcode);
         blockInfo.func = blockInfo.func ? this._sanitizeID(blockInfo.func) : blockInfo.opcode;
         blockInfo.text = blockInfo.text || blockInfo.opcode;
-        blockInfo.func = dispatch.call.bind(dispatch, serviceName, blockInfo.func);
+
+        /**
+         * This is only here because the VM performs poorly when blocks return promises.
+         * @TODO make it possible for the VM to resolve a promise and continue during the same frame.
+         */
+        if (dispatch._isRemoteService(serviceName)) {
+            blockInfo.func = dispatch.call.bind(dispatch, serviceName, blockInfo.func);
+        } else {
+            const serviceObject = dispatch.services[serviceName];
+            blockInfo.func = serviceObject[blockInfo.func].bind(serviceObject);
+        }
         return blockInfo;
     }
 }
diff --git a/src/serialization/sb2_specmap.js b/src/serialization/sb2_specmap.js
index 8f574624b..2024b239e 100644
--- a/src/serialization/sb2_specmap.js
+++ b/src/serialization/sb2_specmap.js
@@ -500,27 +500,27 @@ const specMap = {
         ]
     },
     'clearPenTrails': {
-        opcode: 'pen_clear',
+        opcode: 'pen.clear',
         argMap: [
         ]
     },
     'stampCostume': {
-        opcode: 'pen_stamp',
+        opcode: 'pen.stamp',
         argMap: [
         ]
     },
     'putPenDown': {
-        opcode: 'pen_pendown',
+        opcode: 'pen.penDown',
         argMap: [
         ]
     },
     'putPenUp': {
-        opcode: 'pen_penup',
+        opcode: 'pen.penUp',
         argMap: [
         ]
     },
     'penColor:': {
-        opcode: 'pen_setpencolortocolor',
+        opcode: 'pen.setPenColorToColor',
         argMap: [
             {
                 type: 'input',
@@ -530,7 +530,7 @@ const specMap = {
         ]
     },
     'changePenHueBy:': {
-        opcode: 'pen_changepencolorby',
+        opcode: 'pen.changePenHueBy',
         argMap: [
             {
                 type: 'input',
@@ -540,7 +540,7 @@ const specMap = {
         ]
     },
     'setPenHueTo:': {
-        opcode: 'pen_setpencolortonum',
+        opcode: 'pen.setPenHueToNumber',
         argMap: [
             {
                 type: 'input',
@@ -550,7 +550,7 @@ const specMap = {
         ]
     },
     'changePenShadeBy:': {
-        opcode: 'pen_changepenshadeby',
+        opcode: 'pen.changePenShadeBy',
         argMap: [
             {
                 type: 'input',
@@ -560,7 +560,7 @@ const specMap = {
         ]
     },
     'setPenShadeTo:': {
-        opcode: 'pen_setpenshadeto',
+        opcode: 'pen.setPenShadeToNumber',
         argMap: [
             {
                 type: 'input',
@@ -570,7 +570,7 @@ const specMap = {
         ]
     },
     'changePenSizeBy:': {
-        opcode: 'pen_changepensizeby',
+        opcode: 'pen.changePenSizeBy',
         argMap: [
             {
                 type: 'input',
@@ -580,7 +580,7 @@ const specMap = {
         ]
     },
     'penSize:': {
-        opcode: 'pen_setpensizeto',
+        opcode: 'pen.setPenSizeTo',
         argMap: [
             {
                 type: 'input',
diff --git a/test/integration/pen.js b/test/integration/pen.js
index 25c2121d8..025735bac 100644
--- a/test/integration/pen.js
+++ b/test/integration/pen.js
@@ -1,8 +1,10 @@
+const Worker = require('tiny-worker');
 const path = require('path');
 const test = require('tap').test;
 
 const Scratch3PenBlocks = require('../../src/blocks/scratch3_pen');
 const VirtualMachine = require('../../src/index');
+const dispatch = require('../../src/dispatch/central-dispatch');
 
 const makeTestStorage = require('../fixtures/make-test-storage');
 const extract = require('../fixtures/extract');
@@ -10,6 +12,9 @@ const extract = require('../fixtures/extract');
 const uri = path.resolve(__dirname, '../fixtures/pen.sb2');
 const project = extract(uri);
 
+// By default Central Dispatch works with the Worker class built into the browser. Tell it to use TinyWorker instead.
+dispatch.workerClass = Worker;
+
 test('pen', t => {
     const vm = new VirtualMachine();
     vm.attachStorage(makeTestStorage());
@@ -42,14 +47,16 @@ test('pen', t => {
         vm.clear();
         vm.setCompatibilityMode(false);
         vm.setTurboMode(false);
-        vm.loadProject(project).then(() => {
-            vm.greenFlag();
+        vm.loadProject(project)
+            .then(() => vm.extensionManager.loadExtensionURL('pen')) /** @TODO: loadProject should load extensions */
+            .then(() => {
+                vm.greenFlag();
 
-            // After two seconds, get playground data and stop
-            setTimeout(() => {
-                vm.getPlaygroundData();
-                vm.stopAll();
-            }, 2000);
-        });
+                // After two seconds, get playground data and stop
+                setTimeout(() => {
+                    vm.getPlaygroundData();
+                    vm.stopAll();
+                }, 2000);
+            });
     });
 });