diff --git a/addons/mail/static/src/components/attachment_viewer/attachment_viewer.js b/addons/mail/static/src/components/attachment_viewer/attachment_viewer.js
index 1642e531758..390eac9ebc3 100644
--- a/addons/mail/static/src/components/attachment_viewer/attachment_viewer.js
+++ b/addons/mail/static/src/components/attachment_viewer/attachment_viewer.js
@@ -573,9 +573,9 @@ class AttachmentViewer extends Component {
             return;
         }
         if (ev.deltaY > 0) {
-            this._zoomIn({ scroll: true });
-        } else {
             this._zoomOut({ scroll: true });
+        } else {
+            this._zoomIn({ scroll: true });
         }
     }