diff --git a/src/Interpreters/Cache/FileCache.cpp b/src/Interpreters/Cache/FileCache.cpp
index e9a974bd991..c0becbfbe8d 100644
--- a/src/Interpreters/Cache/FileCache.cpp
+++ b/src/Interpreters/Cache/FileCache.cpp
@@ -676,8 +676,9 @@ bool FileCache::tryReserveImpl(
     if (is_overflow())
         return false;
 
-    for (auto & [_, current_locked_key] : locked)
+    for (auto it = locked.begin(); it != locked.end();)
     {
+        auto & current_locked_key = it->second;
         for (const auto & offset_to_delete : current_locked_key->delete_offsets)
         {
             auto * file_segment_metadata = current_locked_key->getKeyMetadata().getByOffset(offset_to_delete);
@@ -685,6 +686,9 @@ bool FileCache::tryReserveImpl(
             if (query_context)
                 query_context->remove(key, offset);
         }
+
+        /// Do not hold the key lock longer than required.
+        it = locked.erase(it);
     }
 
     if (file_segment_for_reserve)
diff --git a/src/Interpreters/Cache/QueryLimit.h b/src/Interpreters/Cache/QueryLimit.h
index e7f2425eb61..e66c7d2af76 100644
--- a/src/Interpreters/Cache/QueryLimit.h
+++ b/src/Interpreters/Cache/QueryLimit.h
@@ -43,6 +43,7 @@ public:
         const bool recache_on_query_limit_exceeded;
     };
 
+    /// CacheGuard::Lock protects all priority queues.
     class LockedQueryContext
     {
     public: