diff --git a/packages/jspsych/src/ExtensionManager.ts b/packages/jspsych/src/ExtensionManager.ts
index 664162606c..0d627316e6 100644
--- a/packages/jspsych/src/ExtensionManager.ts
+++ b/packages/jspsych/src/ExtensionManager.ts
@@ -4,7 +4,7 @@ import { JsPsychExtension, JsPsychExtensionInfo } from "./modules/extensions";
 import { TrialExtensionsConfiguration } from "./timeline";
 
 export type GlobalExtensionsConfiguration = Array<{
-  type: Class<JsPsychExtension>;
+  type: Class<JsPsychExtension> & { info: JsPsychExtensionInfo };
   params?: Record<string, any>;
 }>;
 
@@ -12,12 +12,16 @@ export interface ExtensionManagerDependencies {
   /**
    * Given an extension class, create a new instance of it and return it.
    */
-  instantiateExtension(extensionClass: Class<JsPsychExtension>): JsPsychExtension;
+  instantiateExtension(
+    extensionClass: Class<JsPsychExtension> & { info: JsPsychExtensionInfo }
+  ): JsPsychExtension;
 }
 
 export class ExtensionManager {
-  private static getExtensionNameByClass(extensionClass: Class<JsPsychExtension>) {
-    return (extensionClass["info"] as JsPsychExtensionInfo).name;
+  private static getExtensionNameByClass(
+    extensionClass: Class<JsPsychExtension> & { info: JsPsychExtensionInfo }
+  ) {
+    return extensionClass.info.name;
   }
 
   public readonly extensions: Record<string, JsPsychExtension>;
@@ -34,7 +38,9 @@ export class ExtensionManager {
     );
   }
 
-  private getExtensionInstanceByClass(extensionClass: Class<JsPsychExtension>) {
+  private getExtensionInstanceByClass(
+    extensionClass: Class<JsPsychExtension> & { info: JsPsychExtensionInfo }
+  ) {
     return this.extensions[ExtensionManager.getExtensionNameByClass(extensionClass)];
   }
 
@@ -43,7 +49,7 @@ export class ExtensionManager {
       this.extensionsConfiguration.map(({ type, params = {} }) => {
         this.getExtensionInstanceByClass(type).initialize(params);
 
-        const extensionInfo = type["info"] as JsPsychExtensionInfo;
+        const extensionInfo = type.info;
 
         if (!("version" in extensionInfo) && !("data" in extensionInfo)) {
           console.warn(
@@ -88,8 +94,10 @@ export class ExtensionManager {
 
     const extensionInfos = trialExtensionsConfiguration.length
       ? {
-          extension_type: trialExtensionsConfiguration.map(({ type }) => type["info"].name),
-          extension_version: trialExtensionsConfiguration.map(({ type }) => type["info"].version),
+          extension_type: trialExtensionsConfiguration.map(({ type }) => type.info.name),
+          extension_version: trialExtensionsConfiguration.map(
+            ({ type }) => type.info.version ?? ""
+          ),
         }
       : {};
 
diff --git a/packages/jspsych/src/modules/extensions.ts b/packages/jspsych/src/modules/extensions.ts
index dd4210a744..c9c60bf352 100644
--- a/packages/jspsych/src/modules/extensions.ts
+++ b/packages/jspsych/src/modules/extensions.ts
@@ -1,3 +1,5 @@
+import { Class } from "type-fest";
+
 import { ParameterInfos } from "./plugins";
 
 export interface JsPsychExtensionInfo {
diff --git a/packages/jspsych/src/timeline/Trial.spec.ts b/packages/jspsych/src/timeline/Trial.spec.ts
index 2a53226257..ebebc87ff2 100644
--- a/packages/jspsych/src/timeline/Trial.spec.ts
+++ b/packages/jspsych/src/timeline/Trial.spec.ts
@@ -615,8 +615,11 @@ describe("Trial", () => {
     it("invokes extension callbacks and includes extension results", async () => {
       dependencies.runOnFinishExtensionCallbacks.mockResolvedValue({ extension: "result" });
 
+      const mockExtensionClass = jest.fn() as any;
+      mockExtensionClass.info = { name: "test-extension", version: "1.0.0" };
+
       const extensionsConfig: TrialExtensionsConfiguration = [
-        { type: jest.fn(), params: { my: "option" } },
+        { type: mockExtensionClass, params: { my: "option" } },
       ];
 
       const trial = createTrial({
@@ -654,9 +657,12 @@ describe("Trial", () => {
         );
       }
 
+      const mockExtensionClass2 = jest.fn() as any;
+      mockExtensionClass2.info = { name: "test-extension-2", version: "1.0.0" };
+
       const trial = createTrial({
         type: TestPlugin,
-        extensions: [{ type: jest.fn(), params: { my: "option" } }],
+        extensions: [{ type: mockExtensionClass2, params: { my: "option" } }],
         on_start: createInvocationOrderCallback("on_start"),
         on_load: createInvocationOrderCallback("on_load"),
         on_finish: createInvocationOrderCallback("on_finish"),
diff --git a/packages/jspsych/src/timeline/index.ts b/packages/jspsych/src/timeline/index.ts
index f929e00ccd..c7c4d364e9 100644
--- a/packages/jspsych/src/timeline/index.ts
+++ b/packages/jspsych/src/timeline/index.ts
@@ -1,6 +1,6 @@
 import { Class } from "type-fest";
 
-import { JsPsychExtension } from "../modules/extensions";
+import { JsPsychExtension, JsPsychExtensionInfo } from "../modules/extensions";
 import { JsPsychPlugin, PluginInfo } from "../modules/plugins";
 import { Trial } from "./Trial";
 import { PromiseWrapper } from "./util";
@@ -12,7 +12,7 @@ export class TimelineVariable {
 export type Parameter<T> = T | (() => T) | TimelineVariable;
 
 export type TrialExtensionsConfiguration = Array<{
-  type: Class<JsPsychExtension>;
+  type: Class<JsPsychExtension> & { info: JsPsychExtensionInfo };
   params?: Record<string, any>;
 }>;