diff --git a/src/gateway/server-methods/wizard.ts b/src/gateway/server-methods/wizard.ts
index 8585a066c..1fab55822 100644
--- a/src/gateway/server-methods/wizard.ts
+++ b/src/gateway/server-methods/wizard.ts
@@ -1,5 +1,6 @@
+import type { ErrorObject } from "ajv";
 import { randomUUID } from "node:crypto";
-import type { GatewayRequestHandlers } from "./types.js";
+import type { GatewayRequestHandlers, RespondFn } from "./types.js";
 import { defaultRuntime } from "../../runtime.js";
 import { WizardSession } from "../../wizard/session.js";
 import {
@@ -13,17 +14,40 @@ import {
 } from "../protocol/index.js";
 import { formatForLog } from "../ws-log.js";
 
+type Validator<T> = ((params: unknown) => params is T) & {
+  errors?: ErrorObject[] | null;
+};
+
+function assertValidParams<T>(
+  params: unknown,
+  validate: Validator<T>,
+  method: string,
+  respond: RespondFn,
+): params is T {
+  if (validate(params)) {
+    return true;
+  }
+  respond(
+    false,
+    undefined,
+    errorShape(
+      ErrorCodes.INVALID_REQUEST,
+      `invalid ${method} params: ${formatValidationErrors(validate.errors)}`,
+    ),
+  );
+  return false;
+}
+
+function readWizardStatus(session: WizardSession) {
+  return {
+    status: session.getStatus(),
+    error: session.getError(),
+  };
+}
+
 export const wizardHandlers: GatewayRequestHandlers = {
   "wizard.start": async ({ params, respond, context }) => {
-    if (!validateWizardStartParams(params)) {
-      respond(
-        false,
-        undefined,
-        errorShape(
-          ErrorCodes.INVALID_REQUEST,
-          `invalid wizard.start params: ${formatValidationErrors(validateWizardStartParams.errors)}`,
-        ),
-      );
+    if (!assertValidParams(params, validateWizardStartParams, "wizard.start", respond)) {
       return;
     }
     const running = context.findRunningWizard();
@@ -47,15 +71,7 @@ export const wizardHandlers: GatewayRequestHandlers = {
     respond(true, { sessionId, ...result }, undefined);
   },
   "wizard.next": async ({ params, respond, context }) => {
-    if (!validateWizardNextParams(params)) {
-      respond(
-        false,
-        undefined,
-        errorShape(
-          ErrorCodes.INVALID_REQUEST,
-          `invalid wizard.next params: ${formatValidationErrors(validateWizardNextParams.errors)}`,
-        ),
-      );
+    if (!assertValidParams(params, validateWizardNextParams, "wizard.next", respond)) {
       return;
     }
     const sessionId = params.sessionId;
@@ -84,15 +100,7 @@ export const wizardHandlers: GatewayRequestHandlers = {
     respond(true, result, undefined);
   },
   "wizard.cancel": ({ params, respond, context }) => {
-    if (!validateWizardCancelParams(params)) {
-      respond(
-        false,
-        undefined,
-        errorShape(
-          ErrorCodes.INVALID_REQUEST,
-          `invalid wizard.cancel params: ${formatValidationErrors(validateWizardCancelParams.errors)}`,
-        ),
-      );
+    if (!assertValidParams(params, validateWizardCancelParams, "wizard.cancel", respond)) {
       return;
     }
     const sessionId = params.sessionId;
@@ -102,23 +110,12 @@ export const wizardHandlers: GatewayRequestHandlers = {
       return;
     }
     session.cancel();
-    const status = {
-      status: session.getStatus(),
-      error: session.getError(),
-    };
+    const status = readWizardStatus(session);
     context.wizardSessions.delete(sessionId);
     respond(true, status, undefined);
   },
   "wizard.status": ({ params, respond, context }) => {
-    if (!validateWizardStatusParams(params)) {
-      respond(
-        false,
-        undefined,
-        errorShape(
-          ErrorCodes.INVALID_REQUEST,
-          `invalid wizard.status params: ${formatValidationErrors(validateWizardStatusParams.errors)}`,
-        ),
-      );
+    if (!assertValidParams(params, validateWizardStatusParams, "wizard.status", respond)) {
       return;
     }
     const sessionId = params.sessionId;
@@ -127,10 +124,7 @@ export const wizardHandlers: GatewayRequestHandlers = {
       respond(false, undefined, errorShape(ErrorCodes.INVALID_REQUEST, "wizard not found"));
       return;
     }
-    const status = {
-      status: session.getStatus(),
-      error: session.getError(),
-    };
+    const status = readWizardStatus(session);
     if (status.status !== "running") {
       context.wizardSessions.delete(sessionId);
     }