diff --git a/src/Storages/StorageReplicatedMergeTree.cpp b/src/Storages/StorageReplicatedMergeTree.cpp
index d08c5b6ad7cbde6447030e9ae4778def39f2501c..2a280508364122c9248aa861d5cad1fc33901ebe 100644
--- a/src/Storages/StorageReplicatedMergeTree.cpp
+++ b/src/Storages/StorageReplicatedMergeTree.cpp
@@ -4151,6 +4151,10 @@ bool StorageReplicatedMergeTree::optimize(
     const Names & deduplicate_by_columns,
     const Context & query_context)
 {
+    /// NOTE: exclusive lock cannot be used here, since this may lead to deadlock (see comments below),
+    /// but it should be safe to use non-exclusive to avoid dropping parts that may be required for processing queue.
+    auto table_lock = lockForShare(query_context.getCurrentQueryId(), query_context.getSettingsRef().lock_acquire_timeout);
+
     assertNotReadonly();
 
     if (!is_leader)