diff --git a/addons/mail/static/src/xml/thread.xml b/addons/mail/static/src/xml/thread.xml
index 50eea76a406..24370c65e4e 100644
--- a/addons/mail/static/src/xml/thread.xml
+++ b/addons/mail/static/src/xml/thread.xml
@@ -53,7 +53,7 @@
                     </div>
                     <img t-if="widget.activeAttachment.fileType === 'image'" class="o_viewer_img" t-attf-src="/web/image/#{widget.activeAttachment.id}?unique=1&amp;signature=#{widget.activeAttachment.checksum}&amp;model=#{model}" alt="Viewer"/>
                     <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 || '').indexOf('text') !== -1" class="mt32 o_viewer_text" t-attf-src="/web/content/#{widget.activeAttachment.id}?model%3D#{model}" />
+                    <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">
                         <source t-attf-src="/web/image/#{widget.activeAttachment.id}?model=#{model}" t-att-data-type="widget.activeAttachment.mimetype"/>
diff --git a/addons/mail/static/tests/document_viewer_tests.js b/addons/mail/static/tests/document_viewer_tests.js
index 404a6f267aa..4d914347669 100644
--- a/addons/mail/static/tests/document_viewer_tests.js
+++ b/addons/mail/static/tests/document_viewer_tests.js
@@ -25,7 +25,7 @@ var createViewer = function (params) {
         if (route === 'https://www.youtube.com/embed/FYqW0Gdwbzk') {
             return Promise.resolve();
         }
-        if (route === '/web/content/4?model%3Dir.attachment') {
+        if (route === '/web/content/4?model=ir.attachment') {
             return Promise.resolve();
         }
         if (route === '/web/image/6?unique=1&signature=999&model=ir.attachment') {
@@ -134,7 +134,7 @@ QUnit.module('DocumentViewer', {
 
         assert.strictEqual(viewer.$(".o_image_caption:contains('text.html')").length, 1,
             "the viewer be on the right attachment");
-        assert.containsOnce(viewer, 'iframe[data-src="/web/content/4?model%3Dir.attachment"]',
+        assert.containsOnce(viewer, 'iframe[data-src="/web/content/4?model=ir.attachment"]',
             "there should be an iframe with the right src");
 
         viewer.destroy();