diff --git a/frontend/src/pages/CourseDetailPage.jsx b/frontend/src/pages/CourseDetailPage.jsx
index 053d711..29336da 100644
--- a/frontend/src/pages/CourseDetailPage.jsx
+++ b/frontend/src/pages/CourseDetailPage.jsx
@@ -193,6 +193,7 @@ export default function CourseDetailPage() {
   }
 
   const markComplete = async (lessonId) => {
+    if (!course.my_enrollment) return
     try {
       await api.put(`/courses/${courseId}/lessons/${lessonId}/progress`, { status: 'completed' })
       setCompletedLessons(prev => { const n = new Set(prev); n.add(lessonId); return n })
@@ -386,12 +387,12 @@ export default function CourseDetailPage() {
               )}
             </div>
             <div style={{ display: 'flex', gap: 8 }}>
-              {!completedLessons.has(activeLesson.id) && (
+              {enrolled && !completedLessons.has(activeLesson.id) && (
                 <button className="btn btn-primary btn-sm" onClick={() => markComplete(activeLesson.id)}>
                   Mark Complete &#10003;
                 </button>
               )}
-              {completedLessons.has(activeLesson.id) && (
+              {enrolled && completedLessons.has(activeLesson.id) && (
                 <span style={{ color: 'var(--correct-fg)', fontWeight: 600, fontSize: '0.88rem', padding: '6px 0' }}>
                   &#10003; Completed
                 </span>
@@ -555,7 +556,7 @@ export default function CourseDetailPage() {
                   lessonId={activeLesson.id}
                   courseId={courseId}
                   onComplete={() => {
-                    if (!completedLessons.has(activeLesson.id)) {
+                    if (enrolled && !completedLessons.has(activeLesson.id)) {
                       markComplete(activeLesson.id)
                     }
                   }}