diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index a8ffc5832a..a0b894602d 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -419,6 +419,7 @@ const char *xcb_protocol_request_codes[] =
 #ifdef Q_XCB_DEBUG
 void QXcbConnection::log(const char *file, int line, int sequence)
 {
+    QMutexLocker locker(&m_callLogMutex);
     CallInfo info;
     info.sequence = sequence;
     info.file = file;
@@ -438,6 +439,7 @@ void QXcbConnection::handleXcbError(xcb_generic_error_t *error)
            int(error->major_code), xcb_protocol_request_codes[clamped_major_code],
            int(error->minor_code));
 #ifdef Q_XCB_DEBUG
+    QMutexLocker locker(&m_callLogMutex);
     int i = 0;
     for (; i < m_callLog.size(); ++i) {
         if (m_callLog.at(i).sequence == error->sequence) {
@@ -459,6 +461,7 @@ void QXcbConnection::handleXcbEvent(xcb_generic_event_t *event)
 {
 #ifdef Q_XCB_DEBUG
     {
+        QMutexLocker locker(&m_callLogMutex);
         int i = 0;
         for (; i < m_callLog.size(); ++i)
             if (m_callLog.at(i).sequence >= event->sequence)
diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index 8c05fe23e4..6d93093072 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -375,6 +375,7 @@ private:
         int line;
     };
     QVector<CallInfo> m_callLog;
+    QMutex m_callLogMutex;
     void log(const char *file, int line, int sequence);
     template <typename cookie_t>
     friend cookie_t q_xcb_call_template(const cookie_t &cookie, QXcbConnection *connection, const char *file, int line);