diff --git a/src/calibre/ebooks/__init__.py b/src/calibre/ebooks/__init__.py
index 4034a8810b..15f172815c 100644
--- a/src/calibre/ebooks/__init__.py
+++ b/src/calibre/ebooks/__init__.py
@@ -103,8 +103,12 @@ def render_html(path_to_html, width=590, height=750):
         loop = QEventLoop()
         renderer = HTMLRenderer(page, loop)
 
-        page.connect(page, SIGNAL('loadFinished(bool)'), renderer)
+        page.connect(page, SIGNAL('loadFinished(bool)'), renderer,
+                Qt.QueuedConnection)
         page.mainFrame().load(QUrl.fromLocalFile(path_to_html))
         loop.exec_()
+    renderer.loop = renderer.page = None
+    del page
+    del loop
     return renderer