diff --git a/pulsar-client-cpp/lib/NegativeAcksTracker.cc b/pulsar-client-cpp/lib/NegativeAcksTracker.cc
index e307091f6c2e8..492e379459393 100644
--- a/pulsar-client-cpp/lib/NegativeAcksTracker.cc
+++ b/pulsar-client-cpp/lib/NegativeAcksTracker.cc
@@ -48,14 +48,14 @@ void NegativeAcksTracker::scheduleTimer() {
 }
 
 void NegativeAcksTracker::handleTimer(const boost::system::error_code &ec) {
-    std::lock_guard<std::mutex> lock(mutex_);
-    timer_ = nullptr;
-
     if (ec) {
         // Ignore cancelled events
         return;
     }
 
+    std::lock_guard<std::mutex> lock(mutex_);
+    timer_ = nullptr;
+
     if (nackedMessages_.empty()) {
         return;
     }