diff -ur qtwebengine-opensource-src-5.9.2/src/core/web_contents_adapter.cpp qtwebengine-opensource-src-5.9.2-qt57/src/core/web_contents_adapter.cpp
--- qtwebengine-opensource-src-5.9.2/src/core/web_contents_adapter.cpp	2017-10-03 11:06:38.000000000 +0200
+++ qtwebengine-opensource-src-5.9.2-qt57/src/core/web_contents_adapter.cpp	2017-11-16 17:17:51.072511997 +0100
@@ -1265,7 +1265,15 @@
     }
 
     const QString &fileName = toQt(dropData.file_description_filename);
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 9, 0))
     const QString &filePath = d->dndTmpDir->filePath(fileName);
+#else
+    QString filePath = d->dndTmpDir->path();
+    if (!filePath.isEmpty()) {
+        filePath += QLatin1Char('/');
+        filePath += fileName;
+    }
+#endif
     QFile file(filePath);
     if (!file.open(QIODevice::WriteOnly)) {
         qWarning("Cannot write temporary file %s.", qUtf8Printable(filePath));