diff --git a/src/core.cpp b/src/core.cpp
index b6b5d9b78..0f3204884 100644
--- a/src/core.cpp
+++ b/src/core.cpp
@@ -39,6 +39,7 @@
 #include <QList>
 #include <QBuffer>
 #include <QMessageBox>
+#include <QMutexLocker>
 
 const QString Core::CONFIG_FILE_NAME = "data";
 const QString Core::TOX_EXT = ".tox";
@@ -768,6 +769,8 @@ void Core::sendGroupMessage(int groupId, const QString& message)
 
 void Core::sendFile(int32_t friendId, QString Filename, QString FilePath, long long filesize)
 {
+    QMutexLocker mlocker(&fileSendMutex);
+
     QByteArray fileName = Filename.toUtf8();
     int fileNum = tox_new_file_sender(tox, friendId, filesize, (uint8_t*)fileName.data(), fileName.size());
     if (fileNum == -1)
diff --git a/src/core.h b/src/core.h
index 301b8525a..8d3821993 100644
--- a/src/core.h
+++ b/src/core.h
@@ -19,6 +19,7 @@
 
 #include <cstdint>
 #include <QObject>
+#include <QMutex>
 
 #include "corestructs.h"
 #include "coreav.h"
@@ -253,6 +254,7 @@ private:
     int dhtServerId;
     static QList<ToxFile> fileSendQueue, fileRecvQueue;
     static ToxCall calls[];
+    QMutex fileSendMutex;
 
     uint8_t* pwsaltedkeys[PasswordType::ptCounter]; // use the pw's hash as the "pw"