diff --git a/src/corelib/io/qfile.cpp b/src/corelib/io/qfile.cpp
index 3a15b4ac7f6..dcb6f5ce4e0 100644
--- a/src/corelib/io/qfile.cpp
+++ b/src/corelib/io/qfile.cpp
@@ -819,7 +819,7 @@ QFile::copy(const QString &newName)
                 const auto fileTemplate = "%1/qt_temp.XXXXXX"_L1;
 #if !QT_CONFIG(temporaryfile)
                 QFile out(fileTemplate.arg(QFileInfo(newName).path()));
-                if (!out.open(QIODevice::ReadWrite))
+                if (!out.open(QIODevice::ReadWrite | QIODevice::Truncate))
                     error = true;
 #else
                 QTemporaryFile out(fileTemplate.arg(QFileInfo(newName).path()));
diff --git a/src/corelib/io/qfilesystemengine_unix.cpp b/src/corelib/io/qfilesystemengine_unix.cpp
index ec962eba365..d19631b9310 100644
--- a/src/corelib/io/qfilesystemengine_unix.cpp
+++ b/src/corelib/io/qfilesystemengine_unix.cpp
@@ -1084,6 +1084,12 @@ bool QFileSystemEngine::cloneFile(int srcfd, int dstfd, const QFileSystemMetaDat
         return false;
     }
 
+    [[maybe_unused]] auto destinationIsEmpty = [dstfd]() {
+        QT_STATBUF statBuffer;
+        return QT_FSTAT(dstfd, &statBuffer) == 0 && statBuffer.st_size == 0;
+    };
+    Q_ASSERT(destinationIsEmpty());
+
 #if defined(Q_OS_LINUX)
     // first, try FICLONE (only works on regular files and only on certain fs)
     if (::ioctl(dstfd, FICLONE, srcfd) == 0)