diff --git a/projects/RabbitMQ.Client/Impl/Channel.PublisherConfirms.cs b/projects/RabbitMQ.Client/Impl/Channel.PublisherConfirms.cs
index 680ac314f..2ba8e0524 100644
--- a/projects/RabbitMQ.Client/Impl/Channel.PublisherConfirms.cs
+++ b/projects/RabbitMQ.Client/Impl/Channel.PublisherConfirms.cs
@@ -295,7 +295,10 @@ await _confirmSemaphore.WaitAsync(cancellationToken)
                 if (_publisherConfirmationTrackingEnabled)
                 {
                     publisherConfirmationTcs = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
-                    _confirmsTaskCompletionSources[publishSequenceNumber] = publisherConfirmationTcs;
+                    if (!_confirmsTaskCompletionSources.TryAdd(publishSequenceNumber, publisherConfirmationTcs))
+                    {
+                        throw new InvalidOperationException($"Failed to track the publisher confirmation for sequence number '{publishSequenceNumber}' because it already exists.");
+                    }
                 }
 
                 _nextPublishSeqNo++;