diff --git a/src/lib/__tests__/llmSchemas.test.js b/src/lib/__tests__/llmSchemas.test.js
index ae79799..deb65c1 100644
--- a/src/lib/__tests__/llmSchemas.test.js
+++ b/src/lib/__tests__/llmSchemas.test.js
@@ -135,7 +135,7 @@ describe('quizQuestionsSchema', () => {
     ).toThrow();
   });
 
-  it('rejects a missing or unknown difficulty', () => {
+  it('falls back to medium for a missing or unknown difficulty', () => {
     const base = {
       id: 'q',
       question: 'q',
@@ -144,10 +144,12 @@ describe('quizQuestionsSchema', () => {
       correctIndex: 0,
       explanation: 'because',
     };
-    expect(() => quizQuestionsSchema.parse({ questions: [base] })).toThrow();
-    expect(() =>
-      quizQuestionsSchema.parse({ questions: [{ ...base, difficulty: 'trivial' }] }),
-    ).toThrow();
+    // Missing difficulty should default to 'medium'
+    const parsed1 = quizQuestionsSchema.parse({ questions: [base] });
+    expect(parsed1.questions[0].difficulty).toBe('medium');
+    // Unknown difficulty should also default to 'medium'
+    const parsed2 = quizQuestionsSchema.parse({ questions: [{ ...base, difficulty: 'trivial' }] });
+    expect(parsed2.questions[0].difficulty).toBe('medium');
   });
 });
 
diff --git a/src/lib/llmSchemas.js b/src/lib/llmSchemas.js
index 6e84f29..63ae60f 100644
--- a/src/lib/llmSchemas.js
+++ b/src/lib/llmSchemas.js
@@ -112,20 +112,32 @@ export const learningAllSchema = z.object({
   infographic: infographicBodySchema,
 });
 
-const quizDifficultyEnum = z.enum(['easy', 'medium', 'hard']);
+const quizDifficultyEnum = z.enum(['easy', 'medium', 'hard']).catch('medium');
 
 const quizQuestionSchema = z.object({
-  id: z.string().min(1),
+  id: z.string().min(1).catch(`gen-${Math.random().toString(36).slice(2, 8)}`),
   question: z.string().min(1),
-  topicLabel: z.string().min(1),
+  topicLabel: z.string().min(1).catch('General'),
   options: z.array(z.string().min(1)).length(4),
-  correctIndex: z.number().int().min(0).max(3),
-  explanation: z.string().min(1),
+  correctIndex: z.preprocess(
+    (v) => (typeof v === 'number' ? Math.round(v) : v),
+    z.number().int().min(0).max(3),
+  ),
+  explanation: z.string().min(1).catch('See the correct answer above.'),
   difficulty: quizDifficultyEnum,
 });
 
 export const quizQuestionsSchema = z.object({
-  questions: z.array(quizQuestionSchema).min(1),
+  questions: z.preprocess(
+    (v) => {
+      // If the model returned an array directly, wrap it
+      if (Array.isArray(v)) return v;
+      // If it returned a single object, wrap in array
+      if (v && typeof v === 'object' && !Array.isArray(v)) return [v];
+      return v;
+    },
+    z.array(quizQuestionSchema).min(1),
+  ),
 });
 
 export const customTopicSchema = z.object({
diff --git a/src/lib/testService.js b/src/lib/testService.js
index 5577e67..38fbadf 100644
--- a/src/lib/testService.js
+++ b/src/lib/testService.js
@@ -79,10 +79,40 @@ Options must be prefixed "A) ", "B) ", "C) ", "D) ". Make questions specific and
   });
 
   const emitted = result.toolUses[0]?.input;
-  if (!emitted?.questions?.length) {
-    throw new Error(`Could not generate questions for ${topic.label}`);
+  if (!emitted) {
+    throw new Error(`LLM did not emit tool output for ${topic.label}`);
   }
-  return emitted.questions;
+
+  // Handle different shapes the LLM might return:
+  // 1. { questions: [...] }  — expected
+  // 2. [...]                 — model returned array directly
+  // 3. { questions: { ... } } — model wrapped single question in object
+  let questions;
+  if (Array.isArray(emitted.questions)) {
+    questions = emitted.questions;
+  } else if (Array.isArray(emitted)) {
+    questions = emitted;
+  } else if (emitted.questions && typeof emitted.questions === 'object') {
+    // Single question wrapped as object instead of array
+    questions = [emitted.questions];
+  } else {
+    throw new Error(`Unexpected quiz output shape for ${topic.label}`);
+  }
+
+  if (!questions.length) {
+    throw new Error(`No questions generated for ${topic.label}`);
+  }
+
+  // Ensure each question has required fields (fill in defaults for missing ones)
+  return questions.map((q, i) => ({
+    id: q.id || `gen-${i}-${Math.random().toString(36).slice(2, 8)}`,
+    question: q.question || '',
+    topicLabel: q.topicLabel || topic.label,
+    options: Array.isArray(q.options) ? q.options.slice(0, 4) : [],
+    correctIndex: typeof q.correctIndex === 'number' ? q.correctIndex : 0,
+    explanation: q.explanation || 'No explanation provided.',
+    difficulty: q.difficulty || 'medium',
+  })).filter(q => q.question && q.options.length === 4);
 }
 
 async function selectTestTopics(userId, isoWeekNumber) {