diff --git a/addons/web/static/src/less/bootstrap_overridden.less b/addons/web/static/src/less/bootstrap_overridden.less
index 0582ec8c384..ada94dbf4ca 100644
--- a/addons/web/static/src/less/bootstrap_overridden.less
+++ b/addons/web/static/src/less/bootstrap_overridden.less
@@ -72,6 +72,19 @@
 @modal-inner-padding: @odoo-horizontal-padding;
 @modal-title-padding: @odoo-horizontal-padding;
 
+// Change the z-index of the modal-backdrop elements to be equal to the
+// modal elements' ones. Bootstrap does not support multi-modals, and without
+// this rule all the modal-backdrops are below all the opened modals.
+// Indeed, bootstrap forces them to a lower z-index as the modal-backdrop
+// element (unique in their supported cases) might be put after the modal
+// element (if the modal is already in the DOM, hidden, then opened). This
+// cannot happen in odoo though as modals are not hidden but removed from
+// the DOM and are always put at the end of the body when opened.
+//
+// Note that the variable @zindex-modal-background may be renamed/removed in
+// newer versions of bootstrap.
+@zindex-modal-background: @zindex-modal;
+
 //== Navs
 @nav-link-padding: 10px 15px;
 @nav-pills-border-radius: 0;
diff --git a/addons/web/static/src/less/modal.less b/addons/web/static/src/less/modal.less
index 95a14420773..ec96d06b67e 100644
--- a/addons/web/static/src/less/modal.less
+++ b/addons/web/static/src/less/modal.less
@@ -77,21 +77,8 @@
     }
 }
 
-// Change the z-index of the modal-backdrop elements to be equal to the
-// modal elements' ones. Bootstrap does not support multi-modals, and without
-// this rule all the modal-backdrops are below all the opened modals.
-// Indeed, bootstrap forces them to a lower z-index as the modal-backdrop
-// element (unique in their supported cases) might be put after the modal
-// element (if the modal is already in the DOM, hidden, then opened). This
-// cannot happen in odoo though as modals are not hidden but removed from
-// the DOM and are always put at the end of the body when opened.
-//
-// Note that the variable @zindex-modal-background may be renamed/removed in
-// newer versions of bootstrap.
-@zindex-modal-background: @zindex-modal;
-
 // Temporary fix for modals which are not instantiated thanks to the Dialog
-// JS classes (deprecated case) + Frontend.
+// JS classes (deprecated case) (see bootstrap_overridden.less) + Frontend.
 :not(body) > .modal {
     z-index: @zindex-modal-background + 1;
 }