diff --git a/libsession/src/main/java/org/session/libsession/messaging/sending_receiving/pollers/Poller.kt b/libsession/src/main/java/org/session/libsession/messaging/sending_receiving/pollers/Poller.kt
index 2b7c8159ea..f0caa9d314 100644
--- a/libsession/src/main/java/org/session/libsession/messaging/sending_receiving/pollers/Poller.kt
+++ b/libsession/src/main/java/org/session/libsession/messaging/sending_receiving/pollers/Poller.kt
@@ -142,8 +142,7 @@ class Poller(private val configFactory: ConfigFactoryProtocol, debounceTimer: Ti
         val messages = rawMessages["messages"] as? List<*>
         val processed = if (!messages.isNullOrEmpty()) {
             SnodeAPI.updateLastMessageHashValueIfPossible(snode, userPublicKey, messages, namespace)
-            SnodeAPI.removeDuplicates(userPublicKey, messages, namespace, true).mapNotNull { messageBody ->
-                val rawMessageAsJSON = messageBody as? Map<*, *> ?: return@mapNotNull null
+            SnodeAPI.removeDuplicates(userPublicKey, messages, namespace, true).mapNotNull { rawMessageAsJSON ->
                 val hashValue = rawMessageAsJSON["hash"] as? String ?: return@mapNotNull null
                 val b64EncodedBody = rawMessageAsJSON["data"] as? String ?: return@mapNotNull null
                 val timestamp = rawMessageAsJSON["t"] as? Long ?: SnodeAPI.nowWithOffset
diff --git a/libsession/src/main/java/org/session/libsession/snode/SnodeAPI.kt b/libsession/src/main/java/org/session/libsession/snode/SnodeAPI.kt
index 9c584ba0fb..72b144be03 100644
--- a/libsession/src/main/java/org/session/libsession/snode/SnodeAPI.kt
+++ b/libsession/src/main/java/org/session/libsession/snode/SnodeAPI.kt
@@ -660,29 +660,33 @@ object SnodeAPI {
         }
     }
 
-    fun removeDuplicates(publicKey: String, rawMessages: List<*>, namespace: Int, updateStoredHashes: Boolean): List<*> {
-        val originalMessageHashValues = database.getReceivedMessageHashValues(publicKey, namespace) ?: emptySet()
-        val receivedMessageHashValues = originalMessageHashValues.toMutableSet()
-        return rawMessages.filter { rawMessage ->
-            (rawMessage as? Map<*, *>)
-                ?.let { it["hash"] as? String }
-                ?.let { receivedMessageHashValues.add(it) }
-                ?: false.also { Log.d("Loki", "Missing hash value for message: ${rawMessage?.prettifiedDescription()}.") }
+    /**
+     *
+     *
+     * TODO Use a db transaction, synchronizing is sufficient for now because
+     * database#setReceivedMessageHashValues is only called here.
+     */
+    @Synchronized
+    fun removeDuplicates(publicKey: String, rawMessages: List<*>, namespace: Int, updateStoredHashes: Boolean): List<Map<*, *>> {
+        val hashValues = database.getReceivedMessageHashValues(publicKey, namespace)?.toMutableSet() ?: mutableSetOf()
+        return rawMessages.filterIsInstance<Map<*, *>>().filter { rawMessage ->
+            val hash = rawMessage["hash"] as? String
+            hash ?: Log.d("Loki", "Missing hash value for message: ${rawMessage.prettifiedDescription()}.")
+            hash?.let(hashValues::add) == true
         }.also {
-            if (updateStoredHashes && originalMessageHashValues.containsAll(receivedMessageHashValues)) {
-                database.setReceivedMessageHashValues(publicKey, receivedMessageHashValues, namespace)
+            if (updateStoredHashes && it.isNotEmpty()) {
+                database.setReceivedMessageHashValues(publicKey, hashValues, namespace)
             }
         }
     }
 
-    private fun parseEnvelopes(rawMessages: List<*>): List<Pair<SignalServiceProtos.Envelope, String?>> = rawMessages.mapNotNull { rawMessage ->
-        val rawMessageAsJSON = rawMessage as? Map<*, *>
-        val base64EncodedData = rawMessageAsJSON?.get("data") as? String
-        val data = base64EncodedData?.let { Base64.decode(it) }
+    private fun parseEnvelopes(rawMessages: List<Map<*, *>>): List<Pair<SignalServiceProtos.Envelope, String?>> = rawMessages.mapNotNull { rawMessage ->
+        val base64EncodedData = rawMessage["data"] as? String
+        val data = base64EncodedData?.let(Base64::decode)
 
-        data ?: Log.d("Loki", "Failed to decode data for message: ${rawMessage?.prettifiedDescription()}.")
+        data ?: Log.d("Loki", "Failed to decode data for message: ${rawMessage.prettifiedDescription()}.")
 
-        data?.runCatching { MessageWrapper.unwrap(this) to rawMessageAsJSON["hash"] as? String }
+        data?.runCatching { MessageWrapper.unwrap(this) to rawMessage["hash"] as? String }
             ?.onFailure { Log.d("Loki", "Failed to unwrap data for message: ${rawMessage.prettifiedDescription()}.") }
             ?.getOrNull()
     }