diff --git a/server/src/main/kotlin/suwayomi/tachidesk/manga/impl/chapter/ChapterForDownload.kt b/server/src/main/kotlin/suwayomi/tachidesk/manga/impl/chapter/ChapterForDownload.kt
index 6b5fe8f0..5222b1e0 100644
--- a/server/src/main/kotlin/suwayomi/tachidesk/manga/impl/chapter/ChapterForDownload.kt
+++ b/server/src/main/kotlin/suwayomi/tachidesk/manga/impl/chapter/ChapterForDownload.kt
@@ -11,6 +11,9 @@ import eu.kanade.tachiyomi.source.model.Page
 import eu.kanade.tachiyomi.source.model.SChapter
 import io.github.oshai.kotlinlogging.KLogger
 import io.github.oshai.kotlinlogging.KotlinLogging
+import io.github.reactivecircus.cache4k.Cache
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import org.jetbrains.exposed.sql.ResultRow
 import org.jetbrains.exposed.sql.SqlExpressionBuilder.eq
 import org.jetbrains.exposed.sql.and
@@ -26,6 +29,7 @@ import suwayomi.tachidesk.manga.model.table.ChapterTable
 import suwayomi.tachidesk.manga.model.table.MangaTable
 import suwayomi.tachidesk.manga.model.table.PageTable
 import suwayomi.tachidesk.manga.model.table.toDataClass
+import kotlin.time.Duration.Companion.minutes
 
 suspend fun getChapterDownloadReady(
     chapterId: Int? = null,
@@ -43,6 +47,12 @@ suspend fun getChapterDownloadReadyByIndex(
     mangaId: Int,
 ): ChapterDataClass = getChapterDownloadReady(chapterIndex = chapterIndex, mangaId = mangaId)
 
+private val mutexByChapterId: Cache<Int, Mutex> =
+    Cache
+        .Builder<Int, Mutex>()
+        .expireAfterAccess(10.minutes)
+        .build()
+
 private class ChapterForDownload(
     optChapterId: Int? = null,
     optChapterIndex: Int? = null,
@@ -69,9 +79,7 @@ private class ChapterForDownload(
 
             markAsNotDownloaded()
 
-            val pageList = fetchPageList()
-
-            updateDatabasePages(pageList)
+            updatePageList()
         }
 
         return asDataClass()
@@ -109,6 +117,14 @@ private class ChapterForDownload(
             }.first()
     }
 
+    private suspend fun updatePageList() {
+        val mutex = mutexByChapterId.get(chapterId) { Mutex() }
+        mutex.withLock {
+            val pageList = fetchPageList()
+            updateDatabasePages(pageList)
+        }
+    }
+
     private suspend fun fetchPageList(): List<Page> {
         val mangaEntry = transaction { MangaTable.selectAll().where { MangaTable.id eq mangaId }.first() }
         val source = getCatalogueSourceOrStub(mangaEntry[MangaTable.sourceReference])
diff --git a/server/src/main/kotlin/suwayomi/tachidesk/server/database/migration/M0045_PreventDuplicatedChapterPages.kt b/server/src/main/kotlin/suwayomi/tachidesk/server/database/migration/M0045_PreventDuplicatedChapterPages.kt
new file mode 100644
index 00000000..e3985bc3
--- /dev/null
+++ b/server/src/main/kotlin/suwayomi/tachidesk/server/database/migration/M0045_PreventDuplicatedChapterPages.kt
@@ -0,0 +1,26 @@
+package suwayomi.tachidesk.server.database.migration
+
+/*
+ * Copyright (C) Contributors to the Suwayomi project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+import de.neonew.exposed.migrations.helpers.SQLMigration
+
+@Suppress("ClassName", "unused")
+class M0045_PreventDuplicatedChapterPages : SQLMigration() {
+    override val sql: String =
+        """
+        DELETE FROM PAGE
+        WHERE ID NOT IN (
+            SELECT MIN(ID)
+            FROM PAGE
+            GROUP BY INDEX, "imageUrl", CHAPTER
+        );
+
+        ALTER TABLE PAGE
+            ADD CONSTRAINT UC_PAGE UNIQUE (INDEX, imageUrl, CHAPTER)
+        """.trimIndent()
+}