diff --git a/client.cpp b/client.cpp
index e815d86..e2889aa 100644
--- a/client.cpp
+++ b/client.cpp
@@ -309,6 +309,9 @@ std::string Client::getKeepAliveInfoString() const
 void Client::resetBuffersIfEligible()
 {
     readbuf.resetSizeIfEligable(initialBufferSize);
+
+    // Write buffers are written to from other threads, and this resetting takes place from the Client's own thread, so we need to lock.
+    std::lock_guard<std::mutex> locker(writeBufMutex);
     writebuf.resetSizeIfEligable(initialBufferSize);
 }