diff --git a/apps/backend/src/lib/workflows.tsx b/apps/backend/src/lib/workflows.tsx
index 655947fad..1817c1cbf 100644
--- a/apps/backend/src/lib/workflows.tsx
+++ b/apps/backend/src/lib/workflows.tsx
@@ -83,7 +83,7 @@ export async function compileWorkflowSource(source: string): Promise<Result<stri
           if (!callbackFunc) {
             throw new Error(\`Callback \${callbackId} not found. Was it maybe deleted from the workflow?\`);
           }
-          return callbackFunc(JSON.parse(data.dataJson));
+          return callbackFunc(data);
         });
         let scheduledCallback = undefined;
         globalThis.scheduleCallback = ({ callbackId, data, scheduleAt }) => {
diff --git a/apps/e2e/tests/backend/workflows.test.ts b/apps/e2e/tests/backend/workflows.test.ts
index 3b62bd304..3b1a0485a 100644
--- a/apps/e2e/tests/backend/workflows.test.ts
+++ b/apps/e2e/tests/backend/workflows.test.ts
@@ -27,23 +27,25 @@ async function configureEmailAndWorkflow(workflowId: string, tsSource: string, e
   });
 }
 
+const waitRetries = 15;
+
 async function waitForMailboxSubject(mailbox: Mailbox, subject: string) {
-  for (let i = 0; i < 15; i++) {
+  for (let i = 0; i < waitRetries; i++) {
     const messages = await mailbox.fetchMessages();
     const message = messages.find((m) => m.subject === subject);
     if (message) return;
     await wait(1_000);
   }
-  throw new Error(`Message with subject ${subject} not found after 15 tries`);
+  throw new Error(`Message with subject ${subject} not found after ${waitRetries} tries`);
 }
 
 async function waitForServerMetadataNotNull(userId: string, key: string) {
-  for (let i = 0; i < 15; i++) {
+  for (let i = 0; i < waitRetries; i++) {
     const user = await niceBackendFetch(`/api/v1/users/${userId}`, { accessType: "server" });
     if (user.body.server_metadata?.[key]) return;
     await wait(1_000);
   }
-  throw new Error(`Server metadata for user ${userId} with key ${key} not found after 15 tries`);
+  throw new Error(`Server metadata for user ${userId} with key ${key} not found after ${waitRetries} tries`);
 }
 
 test("onSignUp workflow sends email for client sign-up", async ({ expect }) => {
@@ -54,8 +56,10 @@ test("onSignUp workflow sends email for client sign-up", async ({ expect }) => {
   await configureEmailAndWorkflow("wf-email", `
     onSignUp(async (user) => {
       await stackApp.sendEmail({ userIds: [user.id], subject: ${JSON.stringify(subject)}, html: "<p>hi</p>" });
+
+      // schedule a callback as an example (we don't actually test whether it executed successfully)
       return scheduleCallback({
-        scheduleAt: new Date(Date.now() + 120_000),
+        scheduleAt: new Date(Date.now() + 7_000),
         data: { "example": "data" },
         callbackId: "my-callback",
       });
@@ -100,6 +104,61 @@ test("onSignUp workflow sends email for client sign-up", async ({ expect }) => {
   timeout: 40_000,
 });
 
+test("onSignUp workflow can schedule callbacks", async ({ expect }) => {
+  await Project.createAndSwitch();
+  const mailbox = await bumpEmailAddress({ unindexed: true });
+  const subject = `WF client signup ${crypto.randomUUID()}`;
+
+  await configureEmailAndWorkflow("wf-email", `
+    onSignUp(async (user) => {
+      return scheduleCallback({
+        scheduleAt: new Date(Date.now() + 7_000),
+        data: { "userId": user.id },
+        callbackId: "my-callback",
+      });
+    });
+
+    registerCallback("my-callback", async (data) => {
+      await stackApp.sendEmail({ userIds: [data.userId], subject: ${JSON.stringify(subject)}, html: "<p>hi</p>" });
+    });
+  `);
+
+  await Auth.Password.signUpWithEmail({ password: "password" });
+
+  // since we wait for the callback, add some extra time
+  await wait(10_000);
+  await waitForMailboxSubject(mailbox, subject);
+
+  expect(await mailbox.fetchMessages()).toMatchInlineSnapshot(`
+    [
+      MailboxMessage {
+        "attachments": [],
+        "body": {
+          "html": "http://localhost:12345/some-callback-url?code=%3Cstripped+query+param%3E",
+          "text": "http://localhost:12345/some-callback-url?code=%3Cstripped+query+param%3E",
+        },
+        "from": "Test Project <test@example.com>",
+        "subject": "Verify your email at New Project",
+        "to": ["<unindexed-mailbox--<stripped UUID>@stack-generated.example.com>"],
+        <some fields may have been hidden>,
+      },
+      MailboxMessage {
+        "attachments": [],
+        "body": {
+          "html": "<!DOCTYPE html PUBLIC \\"-//W3C//DTD XHTML 1.0 Transitional//EN\\" \\"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\\"><html dir=\\"ltr\\" lang=\\"en\\"><head><meta content=\\"text/html; charset=UTF-8\\" http-equiv=\\"Content-Type\\"/><meta name=\\"x-apple-disable-message-reformatting\\"/></head><body style=\\"background-color:rgb(250,251,251);font-family:ui-sans-serif, system-ui, sans-serif, &quot;Apple Color Emoji&quot;, &quot;Segoe UI Emoji&quot;, &quot;Segoe UI Symbol&quot;, &quot;Noto Color Emoji&quot;;font-size:1rem;line-height:1.5rem\\"><!--$--><table align=\\"center\\" width=\\"100%\\" border=\\"0\\" cellPadding=\\"0\\" cellSpacing=\\"0\\" role=\\"presentation\\" style=\\"background-color:rgb(255,255,255);padding:45px;border-radius:0.5rem;max-width:37.5em\\"><tbody><tr style=\\"width:100%\\"><td><div><p>hi</p></div></td></tr></tbody></table><!--7--><!--/$--></body></html>",
+          "text": "hi",
+        },
+        "from": "Test Project <test@example.com>",
+        "subject": "WF client signup <stripped UUID>",
+        "to": ["<unindexed-mailbox--<stripped UUID>@stack-generated.example.com>"],
+        <some fields may have been hidden>,
+      },
+    ]
+  `);
+}, {
+  timeout: 40_000,
+});
+
 test("onSignUp workflow sends email for server-created user", async ({ expect }) => {
   await Project.createAndSwitch();
   await InternalApiKey.createAndSetProjectKeys();
@@ -156,7 +215,7 @@ test("disabled workflows do not trigger", async ({ expect }) => {
 
   await Auth.Password.signUpWithEmail({ password: "password" });
 
-  await wait(18_000);
+  await wait(25_000);
 
   expect(await mailbox.fetchMessages()).toMatchInlineSnapshot(`
     [
@@ -244,7 +303,7 @@ test("anonymous sign-up does not trigger; upgrade triggers workflow", async ({ e
   const { userId: anonUserId } = await Auth.Anonymous.signUp();
 
   // ensure marker not present yet
-  await wait(18_000);
+  await wait(25_000);
   const me1 = await niceBackendFetch("/api/v1/users/me", { accessType: "client" });
   expect(me1.body.server_metadata?.[markerKey]).toBeUndefined();