diff --git a/src/Common/OvercommitTracker.h b/src/Common/OvercommitTracker.h
index 267ba13aecb..37de75f4848 100644
--- a/src/Common/OvercommitTracker.h
+++ b/src/Common/OvercommitTracker.h
@@ -155,11 +155,15 @@ private:
     Poco::Logger * logger = &Poco::Logger::get("GlobalOvercommitTracker");
 };
 
+// This class is used to disallow tracking during logging to avoid deadlocks.
 struct OvercommitTrackerBlockerInThread
 {
     OvercommitTrackerBlockerInThread() { ++counter; }
     ~OvercommitTrackerBlockerInThread() { --counter; }
 
+    OvercommitTrackerBlockerInThread(OvercommitTrackerBlockerInThread const &) = delete;
+    OvercommitTrackerBlockerInThread & operator=(OvercommitTrackerBlockerInThread const &) = delete;
+
     static bool isBlocked() { return counter > 0; }
 
 private: