diff --git a/src/engine/runtime.js b/src/engine/runtime.js
index 7daa4c4e40..016d3d6510 100644
--- a/src/engine/runtime.js
+++ b/src/engine/runtime.js
@@ -1061,7 +1061,25 @@ class Runtime extends EventEmitter {
      * @param {ExtensionMetadata} extensionInfo - information about the extension (id, blocks, etc.)
      * @private
      */
-    _registerExtensionPrimitives (extensionInfo) {
+    async _registerExtensionPrimitives (extensionInfo) {
+
+        // If the extension requires other extensions, load them first.
+        if (Array.isArray(extensionInfo.requiredExtensions)) {
+            for (const extensionId of extensionInfo.requiredExtensions) {
+                if (
+                    this.extensionManager.isCoreExtension(extensionId) ||
+                    this.extensionManager.isBuiltinExtension(extensionId) ||
+                    await this.extensionManager.securityManager.canLoadExtensionFromProject(extensionId)
+                ) {
+                    this.extensionManager.loadExtensionURL(extensionId);
+                } else {
+                    console.warn(
+                        `Failed to load required extension: ${extensionId} for extension: ${extensionInfo.id}`
+                    );
+                }
+            }
+        }
+
         const categoryInfo = {
             id: extensionInfo.id,
             name: maybeFormatMessage(extensionInfo.name),
diff --git a/src/extension-support/extension-manager.js b/src/extension-support/extension-manager.js
index edcea24ecf..fba1d3a434 100644
--- a/src/extension-support/extension-manager.js
+++ b/src/extension-support/extension-manager.js
@@ -29,6 +29,20 @@ const defaultBuiltinExtensions = {
     tw: () => require('../extensions/tw')
 };
 
+const coreExtensions = [
+    'motion',
+    'looks',
+    'sound',
+    'events',
+    'control',
+    'sensing',
+    'operators',
+    'data',
+    'json',
+    'procedures',
+    'comments'
+];
+
 /**
  * @typedef {object} ArgumentInfo - Information about an extension block argument
  * @property {ArgumentType} type - the type of value this argument can take
@@ -126,6 +140,7 @@ class ExtensionManager {
         this.asyncExtensionsLoadedCallbacks = [];
 
         this.builtinExtensions = Object.assign({}, defaultBuiltinExtensions);
+        this.coreExtensions = coreExtensions;
 
         dispatch.setService('extensions', createExtensionService(this)).catch(e => {
             log.error(`ExtensionManager was unable to register extension service: ${JSON.stringify(e)}`);
@@ -153,6 +168,16 @@ class ExtensionManager {
         return Object.prototype.hasOwnProperty.call(this.builtinExtensions, extensionId);
     }
 
+    /**
+     * Determine whether an extension with a given ID is registered as a core extension in the VM, such as motion.
+     * Note that custom extensions or extensions that don't load on startup will return false here.
+     * @param {string} extensionId
+     * @returns {boolean}
+     */
+    isCoreExtension (extensionId) {
+        return this.coreExtensions.includes(extensionId);
+    }
+
     /**
      * Synchronously load an internal extension (core or non-core) by ID. This call will
      * fail if the provided id is not does not match an internal extension.
@@ -207,8 +232,8 @@ class ExtensionManager {
             return;
         }
 
-        if (this.isExtensionURLLoaded(extensionURL)) {
-            // Extension is already loaded.
+        if (this.isExtensionURLLoaded(extensionURL) || this.isCoreExtension(extensionURL)) {
+            // Extension is already loaded or is a core extension.
             return;
         }