diff --git a/lib/megacloud-extractor/src/main/java/eu/kanade/tachiyomi/lib/megacloudextractor/MegaCloudExtractor.kt b/lib/megacloud-extractor/src/main/java/eu/kanade/tachiyomi/lib/megacloudextractor/MegaCloudExtractor.kt
index cfa01bf12..26c9c7331 100644
--- a/lib/megacloud-extractor/src/main/java/eu/kanade/tachiyomi/lib/megacloudextractor/MegaCloudExtractor.kt
+++ b/lib/megacloud-extractor/src/main/java/eu/kanade/tachiyomi/lib/megacloudextractor/MegaCloudExtractor.kt
@@ -4,16 +4,20 @@ import eu.kanade.tachiyomi.animesource.model.Track
 import eu.kanade.tachiyomi.animesource.model.Video
 import eu.kanade.tachiyomi.lib.cryptoaes.CryptoAES
 import eu.kanade.tachiyomi.lib.playlistutils.PlaylistUtils
-import okhttp3.Headers
 import eu.kanade.tachiyomi.network.GET
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import kotlinx.serialization.Serializable
 import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.jsonPrimitive
+import okhttp3.CacheControl
+import okhttp3.Headers
+import okhttp3.HttpUrl.Companion.toHttpUrl
 import okhttp3.OkHttpClient
 import uy.kohesive.injekt.injectLazy
-import kotlinx.serialization.Serializable
-import kotlinx.serialization.json.JsonElement
-import okhttp3.CacheControl
-import okhttp3.HttpUrl.Companion.toHttpUrl
 
 class MegaCloudExtractor(private val client: OkHttpClient, private val headers: Headers) {
     private val json: Json by injectLazy()
@@ -30,16 +34,26 @@ class MegaCloudExtractor(private val client: OkHttpClient, private val headers:
         private val SOURCES_URL = arrayOf("/embed-2/ajax/e-1/getSources?id=", "/ajax/embed-6-v2/getSources?id=")
         private val SOURCES_SPLITTER = arrayOf("/e-1/", "/embed-6-v2/")
         private val SOURCES_KEY = arrayOf("1", "6")
+        private val INDEX_PAIRS_MAP = mutableMapOf("1" to emptyList<List<Int>>(), "6" to emptyList<List<Int>>())
+        private val MUTEX = Mutex()
+
+        private inline fun <reified R> runLocked(crossinline block: () -> R) = runBlocking(Dispatchers.IO) {
+            MUTEX.withLock { block() }
+        }
+    }
+
+    private fun getIndexPairs(type: String) = runLocked {
+        INDEX_PAIRS_MAP[type].orEmpty().ifEmpty {
+            noCacheClient.newCall(GET("https://raw.githubusercontent.com/Claudemirovsky/keys/e$type/key", cache = cacheControl))
+                .execute()
+                .use { it.body.string() }
+                .let { json.decodeFromString<List<List<Int>>>(it) }
+                .also { INDEX_PAIRS_MAP[type] = it }
+        }
     }
 
     private fun cipherTextCleaner(data: String, type: String): Pair<String, String> {
-        // TODO: fetch the key only when needed, using a thread-safe map
-        // (Like ConcurrentMap?) or MUTEX hacks.
-        val indexPairs = noCacheClient.newCall(GET("https://raw.githubusercontent.com/Claudemirovsky/keys/e$type/key", cache = cacheControl))
-            .execute()
-            .use { it.body.string() }
-            .let { json.decodeFromString<List<List<Int>>>(it) }
-
+        val indexPairs = getIndexPairs(type)
         val (password, ciphertext, _) = indexPairs.fold(Triple("", data, 0)) { previous, item ->
             val start = item.first() + previous.third
             val end = start + item.last()
@@ -56,6 +70,8 @@ class MegaCloudExtractor(private val client: OkHttpClient, private val headers:
         if (attempts > 2) throw Exception("PLEASE NUKE ANIWATCH AND CLOUDFLARE")
         val (ciphertext, password) = cipherTextCleaner(ciphered, type)
         return CryptoAES.decrypt(ciphertext, password).ifEmpty {
+            // Update index pairs
+            runLocked { INDEX_PAIRS_MAP[type] = emptyList<List<Int>>() }
             tryDecrypting(ciphered, type, attempts + 1)
         }
     }
@@ -67,7 +83,7 @@ class MegaCloudExtractor(private val client: OkHttpClient, private val headers:
         val subs2 = video.tracks
             ?.filter { it.kind == "captions" }
             ?.map { Track(it.file, it.label) }
-            ?: emptyList()
+            .orEmpty()
         return playlistUtils.extractFromHls(
             masterUrl,
             videoNameGen = { "$name - $it - $type" },