diff --git a/addons/mail/static/src/core/common/attachment_model.js b/addons/mail/static/src/core/common/attachment_model.js
index 159a7c30419..66cf0af33fd 100644
--- a/addons/mail/static/src/core/common/attachment_model.js
+++ b/addons/mail/static/src/core/common/attachment_model.js
@@ -53,7 +53,7 @@ export class Attachment {
     }
 
     get isPdf() {
-        return this.mimetype === "application/pdf";
+        return this.mimetype && this.mimetype.startsWith("application/pdf");
     }
 
     get isImage() {