diff --git a/autotests/kfiledialog_unittest.cpp b/autotests/kfiledialog_unittest.cpp
--- a/autotests/kfiledialog_unittest.cpp
+++ b/autotests/kfiledialog_unittest.cpp
@@ -111,6 +111,16 @@
 
         QCOMPARE(dialog.selectedMimeTypeFilter(), targetMimeTypeFilter);
     }
+
+    void testFallbackOnFirstFilterInSaveMode()
+    {
+        QFileDialog dialog;
+        dialog.setAcceptMode(QFileDialog::AcceptSave);
+        dialog.setMimeTypeFilters({QStringLiteral("application/json"), QStringLiteral("application/zip")});
+        dialog.show();
+        QCOMPARE(dialog.selectedMimeTypeFilter(), QStringLiteral("application/json"));
+    }
+
 #endif
 
 
diff --git a/src/platformtheme/kdeplatformfiledialoghelper.cpp b/src/platformtheme/kdeplatformfiledialoghelper.cpp
--- a/src/platformtheme/kdeplatformfiledialoghelper.cpp
+++ b/src/platformtheme/kdeplatformfiledialoghelper.cpp
@@ -298,7 +298,16 @@
         const QStringList mimeFilters = options()->mimeTypeFilters();
         const QStringList nameFilters = options()->nameFilters();
         if (!mimeFilters.isEmpty()) {
-            dialog->m_fileWidget->setMimeFilter(mimeFilters);
+            QString defaultMimeFilter;
+            if (options()->acceptMode() == QFileDialogOptions::AcceptSave) {
+#if QT_VERSION >= QT_VERSION_CHECK(5, 9, 0)
+                defaultMimeFilter = options()->initiallySelectedMimeTypeFilter();
+#endif
+                if (defaultMimeFilter.isEmpty()) {
+                    defaultMimeFilter = mimeFilters.at(0);
+                }
+            }
+            dialog->m_fileWidget->setMimeFilter(mimeFilters, defaultMimeFilter);
 
             if ( mimeFilters.contains( QStringLiteral("inode/directory") ) )
                 dialog->m_fileWidget->setMode( dialog->m_fileWidget->mode() | KFile::Directory );