diff --git a/src/app/admin/courses/[courseId]/modules/[moduleId]/lessons/[lessonId]/page.tsx b/src/app/admin/courses/[courseId]/modules/[moduleId]/lessons/[lessonId]/page.tsx
index 560fd42..7522b69 100644
--- a/src/app/admin/courses/[courseId]/modules/[moduleId]/lessons/[lessonId]/page.tsx
+++ b/src/app/admin/courses/[courseId]/modules/[moduleId]/lessons/[lessonId]/page.tsx
@@ -36,6 +36,17 @@ export default async function LessonEditorPage({ params }: Props) {
   const prevLesson = idx > 0 ? siblings[idx - 1] : null;
   const nextLesson = idx < siblings.length - 1 ? siblings[idx + 1] : null;
 
+  // Serialize all Prisma proxy objects (DateTime, relations) before passing to Client Components
+  const plain = JSON.parse(JSON.stringify({
+    files: lesson.files,
+    homework: lesson.homework,
+    siblings,
+  })) as {
+    files: typeof lesson.files;
+    homework: typeof lesson.homework;
+    siblings: typeof siblings;
+  };
+
   return (
     <div className="p-8 max-w-4xl">
       <nav className="text-xs mb-6 uppercase tracking-widest" style={{ color: "var(--muted-foreground)" }}>
@@ -61,8 +72,8 @@ export default async function LessonEditorPage({ params }: Props) {
           courseId={courseId}
           moduleId={moduleId}
           courseSlug={lesson.module.course.slug}
-          prevLesson={prevLesson}
-          nextLesson={nextLesson}
+          prevLesson={plain.siblings[idx - 1] ?? null}
+          nextLesson={plain.siblings[idx + 1] ?? null}
         />
       </div>
 
@@ -71,7 +82,7 @@ export default async function LessonEditorPage({ params }: Props) {
         <p className="text-xs font-bold uppercase tracking-widest mb-4" style={{ color: "var(--muted-foreground)" }}>
           Файлы и материалы
         </p>
-        <LessonFilesManager lessonId={lessonId} initialFiles={lesson.files} />
+        <LessonFilesManager lessonId={lessonId} initialFiles={plain.files} />
       </div>
 
       {/* Homework section */}
@@ -79,7 +90,7 @@ export default async function LessonEditorPage({ params }: Props) {
         <p className="text-xs font-bold uppercase tracking-widest mb-4" style={{ color: "var(--muted-foreground)" }}>
           Домашнее задание
         </p>
-        <HomeworkEditor lessonId={lessonId} initial={lesson.homework} />
+        <HomeworkEditor lessonId={lessonId} initial={plain.homework} />
       </div>
     </div>
   );
diff --git a/src/app/admin/courses/[courseId]/modules/[moduleId]/page.tsx b/src/app/admin/courses/[courseId]/modules/[moduleId]/page.tsx
index 1f635d0..b037c4b 100644
--- a/src/app/admin/courses/[courseId]/modules/[moduleId]/page.tsx
+++ b/src/app/admin/courses/[courseId]/modules/[moduleId]/page.tsx
@@ -30,6 +30,11 @@ export default async function ModulePage({ params }: Props) {
 
   if (!module || module.courseId !== courseId) notFound();
 
+  const plain = JSON.parse(JSON.stringify({ lessons: module.lessons, allModules })) as {
+    lessons: typeof module.lessons;
+    allModules: typeof allModules;
+  };
+
   return (
     <div className="p-8 max-w-3xl">
       <nav className="text-xs mb-6 uppercase tracking-widest" style={{ color: "var(--muted-foreground)" }}>
@@ -54,8 +59,8 @@ export default async function ModulePage({ params }: Props) {
         <SortableLessons
           courseId={courseId}
           moduleId={moduleId}
-          lessons={module.lessons}
-          otherModules={allModules}
+          lessons={plain.lessons}
+          otherModules={plain.allModules}
         />
       </section>
     </div>