diff --git a/lib/csp.js b/lib/csp.js
index b343ea011..c54007646 100644
--- a/lib/csp.js
+++ b/lib/csp.js
@@ -8,7 +8,7 @@ const defaultDirectives = {
   baseUri: ['\'self\''],
   connectSrc: ['\'self\''],
   fontSrc: ['\'self\''],
-  frameSrc: ['https://player.vimeo.com', 'https://www.slideshare.net/slideshow/embed_code/key/', 'https://www.youtube.com'],
+  frameSrc: ['\'self\'', 'https://player.vimeo.com', 'https://www.slideshare.net/slideshow/embed_code/key/', 'https://www.youtube.com'],
   imgSrc: ['*'], // we allow using arbitrary images
   scriptSrc: [
     config.serverURL + '/build/',