diff --git a/addons/mail/static/src/xml/thread.xml b/addons/mail/static/src/xml/thread.xml
index bf1c5427911..05f9f04f6f7 100644
--- a/addons/mail/static/src/xml/thread.xml
+++ b/addons/mail/static/src/xml/thread.xml
@@ -61,7 +61,7 @@
                         <t t-set="unique" t-value="widget.activeAttachment.checksum ? widget.activeAttachment.checksum.slice(-8) : ''"/>
                         <img class="o_viewer_img" t-attf-src="/web/image/#{widget.activeAttachment.id}?unique=#{unique}&amp;model=#{model}" alt="Viewer"/>
                     </t>
-                    <iframe t-if="widget.activeAttachment.fileType == 'application/pdf'" class="mt32 o_viewer_pdf"  t-attf-src="/web/static/lib/pdfjs/web/viewer.html?file=/web/content/#{widget.activeAttachment.id}?model%3D#{model}" />
+                    <iframe t-if="widget.activeAttachment.fileType == 'application/pdf'" class="mt32 o_viewer_pdf"  t-attf-src="/web/static/lib/pdfjs/web/viewer.html?file=/web/content/#{widget.activeAttachment.id}?model%3D#{model}%26filename%3D#{window.encodeURIComponent(widget.activeAttachment.name)}" />
                     <iframe t-if="(widget.activeAttachment.fileType || '').indexOf('text') !== -1" class="mt32 o_viewer_text" t-attf-src="/web/content/#{widget.activeAttachment.id}?model=#{model}" />
                     <iframe t-if="widget.activeAttachment.fileType == 'youtu'" class="mt32 o_viewer_text"  allow="autoplay; encrypted-media" width="560" height="315" t-attf-src="https://www.youtube.com/embed/#{widget.activeAttachment.youtube}"/>
                     <video t-if="widget.activeAttachment.fileType == 'video'" class="o_viewer_video" controls="controls">
diff --git a/addons/mail/static/tests/document_viewer_tests.js b/addons/mail/static/tests/document_viewer_tests.js
index 5ccb9df5ff3..aa50483b48a 100644
--- a/addons/mail/static/tests/document_viewer_tests.js
+++ b/addons/mail/static/tests/document_viewer_tests.js
@@ -19,7 +19,7 @@ var createViewer = function (params) {
     var viewer = new DocumentViewer(parent, params.attachments, params.attachmentID);
 
     var mockRPC = function (route) {
-        if (route === '/web/static/lib/pdfjs/web/viewer.html?file=/web/content/1?model%3Dir.attachment') {
+        if (route === '/web/static/lib/pdfjs/web/viewer.html?file=/web/content/1?model%3Dir.attachment%26filename%3DfilePdf.pdf') {
             return Promise.resolve();
         }
         if (route === 'https://www.youtube.com/embed/FYqW0Gdwbzk') {