diff --git a/setup/installer/windows/file_dialogs.cpp b/setup/installer/windows/file_dialogs.cpp
index ee10aef947..56b4557900 100644
--- a/setup/installer/windows/file_dialogs.cpp
+++ b/setup/installer/windows/file_dialogs.cpp
@@ -25,7 +25,10 @@ int show_dialog(HWND parent, bool save_dialog, LPWSTR title) {
 	hr = CoInitialize(NULL);
 	if (FAILED(hr)) { PRINTERR("Failed to initialize COM"); return 1; }
 
-	CALLCOM(CoCreateInstance(CLSID_FileOpenDialog, NULL, CLSCTX_INPROC_SERVER, (save_dialog ? IID_IFileSaveDialog : IID_IFileOpenDialog), reinterpret_cast<LPVOID*>(&pfd)), "Failed to create COM object for file dialog")
+	CALLCOM(CoCreateInstance((save_dialog ? CLSID_FileSaveDialog : CLSID_FileOpenDialog),
+				NULL, CLSCTX_INPROC_SERVER, (save_dialog ? IID_IFileSaveDialog : IID_IFileOpenDialog),
+				reinterpret_cast<LPVOID*>(&pfd)),
+		"Failed to create COM object for file dialog")
 	CALLCOM(pfd->GetOptions(&dwFlags), "Failed to get options")
 	dwFlags |= FOS_FORCEFILESYSTEM;
 	CALLCOM(pfd->SetOptions(dwFlags), "Failed to set options")
@@ -107,6 +110,8 @@ int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine
 
 		else if CHECK_KEY("TITLE") { READSTR(title) }
 
+		else if CHECK_KEY("SAVE_AS") { READ(1, buf); save_dialog = !!buf[0]; }
+
 		else {
 			PRINTERR("Unknown key");
 			return 1;
diff --git a/src/calibre/gui2/win_file_dialogs.py b/src/calibre/gui2/win_file_dialogs.py
index 858b95c996..9da340f621 100644
--- a/src/calibre/gui2/win_file_dialogs.py
+++ b/src/calibre/gui2/win_file_dialogs.py
@@ -26,6 +26,10 @@ def serialize_hwnd(hwnd):
         return b''
     return struct.pack(b'=' + (b'B4sQ' if is64bit else b'I'), 4, b'HWND', int(hwnd))
 
+def serialize_binary(key, val):
+    key = key.encode('ascii') if not isinstance(key, bytes) else key
+    return struct.pack(b'=B%ssB' % len(key), len(key), key, int(val))
+
 def serialize_string(key, val):
     key = key.encode('ascii') if not isinstance(key, bytes) else key
     val = type('')(val).encode('utf-8')
@@ -57,12 +61,14 @@ class Loop(QEventLoop):
         QEventLoop.__init__(self)
         self.dialog_closed.connect(self.exit, type=Qt.QueuedConnection)
 
-def run_file_dialog(parent=None, title=None):
+def run_file_dialog(parent=None, title=None, save_as=False):
     data = []
     if parent is not None:
         data.append(serialize_hwnd(get_hwnd(parent)))
     if title is not None:
         data.append(serialize_string('TITLE', title))
+    if save_as:
+        data.append(serialize_binary('SAVE_AS', save_as))
     loop = Loop()
     h = Helper(subprocess.Popen(
         [HELPER], stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE),
@@ -81,7 +87,7 @@ if __name__ == '__main__':
     q = QMainWindow()
 
     def clicked():
-        print(run_file_dialog(b, 'Testing dialogs')), sys.stdout.flush()
+        print(run_file_dialog(b, 'Testing dialogs', True)), sys.stdout.flush()
 
     b = QPushButton('click me')
     b.clicked.connect(clicked)