diff --git a/frontend/locales/en.json b/frontend/locales/en.json
index c16b77139..da0b553d9 100644
--- a/frontend/locales/en.json
+++ b/frontend/locales/en.json
@@ -258,6 +258,8 @@
       "password_confirm_label": "Confirm password",
       "password_label": "Password",
       "passwordless_notice": "This account doesn't need a password. We'll send a verification code to your email address instead.",
+      "pinned_email_error": "This invite's email address can't be used to create an account. Let whoever invited you know.",
+      "pinned_username_error": "The account this invite is for can't be created. Let whoever invited you know.",
       "send_code": "Send code",
       "terms_of_service": "I agree to the <a>Terms and Conditions</a>",
       "username_available": "This username is available",
diff --git a/frontend/src/components/RegisterForm/RegisterForm.tsx b/frontend/src/components/RegisterForm/RegisterForm.tsx
index 321991532..1f58e154b 100644
--- a/frontend/src/components/RegisterForm/RegisterForm.tsx
+++ b/frontend/src/components/RegisterForm/RegisterForm.tsx
@@ -211,6 +211,15 @@ export const PasswordRegisterForm: React.FC<{
         <ErrorAlert>{t("frontend.register.invite_invalid")}</ErrorAlert>
       )}
 
+      {/* The user never chose a pinned value, so its errors get their own words */}
+      {pinnedUsername && !!fields.username?.errors.length && (
+        <ErrorAlert>{t("frontend.register.pinned_username_error")}</ErrorAlert>
+      )}
+
+      {pinnedEmail && !!fields.email?.errors.length && (
+        <ErrorAlert>{t("frontend.register.pinned_email_error")}</ErrorAlert>
+      )}
+
       {formErrors.map((error, index) => (
         <div
           // biome-ignore lint/suspicious/noArrayIndexKey: the server error list is static
diff --git a/frontend/src/entrypoints/register.test.tsx b/frontend/src/entrypoints/register.test.tsx
index e07915568..7356887d1 100644
--- a/frontend/src/entrypoints/register.test.tsx
+++ b/frontend/src/entrypoints/register.test.tsx
@@ -120,4 +120,64 @@ describe("register island", () => {
       ).toBeTruthy();
     });
   });
+
+  describe("with an invite pinning the username and email", () => {
+    const invite = {
+      valid: true,
+      username: "alice",
+      email: "alice@example.com",
+      passwordless: true,
+    };
+
+    it("explains an error on the username above the form", async () => {
+      await mountRegister({
+        invite,
+        form: {
+          errors: [],
+          fields: { username: { value: "", errors: [{ kind: "exists" }] } },
+        },
+      });
+
+      const alert = screen.getByRole("alert");
+      expect(alert).toHaveTextContent(
+        "The account this invite is for can't be created.",
+      );
+      expect(
+        alert.compareDocumentPosition(
+          screen.getByRole("button", { name: "Send code" }),
+        ) & Node.DOCUMENT_POSITION_FOLLOWING,
+      ).toBeTruthy();
+    });
+
+    it("explains an error on the email address above the form", async () => {
+      await mountRegister({
+        invite,
+        form: {
+          errors: [],
+          fields: {
+            email: {
+              value: "alice@example.com",
+              errors: [
+                {
+                  kind: "policy",
+                  code: "email-domain-banned",
+                  message: "Email domain is banned",
+                },
+              ],
+            },
+          },
+        },
+      });
+
+      const alert = screen.getByRole("alert");
+      expect(alert).toHaveTextContent(
+        "This invite's email address can't be used to create an account.",
+      );
+      expect(
+        alert.compareDocumentPosition(
+          screen.getByRole("button", { name: "Send code" }),
+        ) & Node.DOCUMENT_POSITION_FOLLOWING,
+      ).toBeTruthy();
+    });
+  });
 });