diff --git a/addons/hr_timesheet_sheet/static/src/less/timesheet.less b/addons/hr_timesheet_sheet/static/src/less/timesheet.less
index 86f106e6078..611042f087b 100644
--- a/addons/hr_timesheet_sheet/static/src/less/timesheet.less
+++ b/addons/hr_timesheet_sheet/static/src/less/timesheet.less
@@ -28,9 +28,6 @@
                 .oe_timesheet_button_add {
                     margin-left: 8px;
                 }
-                .o_with_button + .oe_timesheet_button_add {
-                    margin-left: 45px;
-                }
             }
 
             .oe_timesheet_weekly_today {
@@ -47,7 +44,7 @@
                 > div {
                     .o-flex-display();
                     .o-align-items(center);
-                    
+
                     .o_field_many2one {
                         min-width: 200px;
                         margin: 0;
@@ -62,9 +59,6 @@
                         .o-flex(0, 0, auto);
                         margin-left: 8px;
                     }
-                    .o_with_button + .oe_timesheet_button_add {
-                        margin-left: 45px;
-                    }
                 }
             }
         }
diff --git a/addons/web/static/src/js/fields/relational_fields.js b/addons/web/static/src/js/fields/relational_fields.js
index 194165b2206..9218897fb1f 100644
--- a/addons/web/static/src/js/fields/relational_fields.js
+++ b/addons/web/static/src/js/fields/relational_fields.js
@@ -422,7 +422,7 @@ var FieldMany2One = AbstractField.extend({
     _updateExternalButton: function () {
         var has_external_button = !this.nodeOptions.no_open && !this.floating && this.isSet();
         this.$external_button.toggle(has_external_button);
-        this.$el.toggleClass('o_with_button', has_external_button);
+        this.$el.toggleClass('o_with_button', has_external_button); // Should not be required anymore but kept for compatibility
     },
 
 
diff --git a/addons/web/static/src/less/fields.less b/addons/web/static/src/less/fields.less
index 02885ef3514..fe7a4ad0d8e 100644
--- a/addons/web/static/src/less/fields.less
+++ b/addons/web/static/src/less/fields.less
@@ -49,7 +49,7 @@
 
     // Dropdowns input (many2one, ...)
     .o_input_dropdown {
-        .o-flex(1, 0, auto);
+        .o-flex(1, 1, auto);
         position: relative;
         width: 100%;
 
@@ -185,14 +185,6 @@
         color: @brand-success;
     }
 
-    // Many2One
-    &.o_field_many2one {
-        .o-inline-flex-display();
-        > span, > button {
-            .o-flex(0, 0, auto);
-        }
-    }
-
     // Handle widget
     &.o_row_handle {
         cursor: ns-resize;
diff --git a/addons/web/static/src/less/form_view.less b/addons/web/static/src/less/form_view.less
index c4990e6c824..7224ff5c20d 100644
--- a/addons/web/static/src/less/form_view.less
+++ b/addons/web/static/src/less/form_view.less
@@ -64,12 +64,6 @@
                 .o-align-self(center);
             }
         }
-
-        .o_row .o_field_many2one, .o_field_many2one.oe_inline {
-            &.o_with_button:not(:last-child) { // If invisible element as last child, this line has no effect but that's not very important
-                margin-right: (35px + (@odoo-form-spacing-unit/2));
-            }
-        }
     }
 
     .o_row > div > .o_field_widget {
@@ -338,6 +332,17 @@
             }
         }
 
+        :not(.o_row) > .o_field_widget,
+        .o_row > .o_field_widget:last-child { // Note: this does not take care
+                                              // of an invisible last-child but
+                                              // it does not really matter
+            // Makes extra buttons (e.g. m2o external button) overflow on the
+            // right padding of the parent element
+            .o_input_dropdown {
+                .o-flex(1, 0, auto);
+            }
+        }
+
         &.o_label_nowrap .o_form_label {
             white-space: nowrap;
         }
diff --git a/addons/web/static/src/less/list_view.less b/addons/web/static/src/less/list_view.less
index d84f673ab75..4a5429c6de2 100644
--- a/addons/web/static/src/less/list_view.less
+++ b/addons/web/static/src/less/list_view.less
@@ -153,9 +153,6 @@
         .o_field_widget {
             min-width: 0;
         }
-        .o_with_button .o_input_dropdown {
-            width: 1%; // Hack so that the sibling button is not overlapped
-        }
         .o_input_dropdown, .o_datepicker {
             > .o_input {
                 padding-right: 15px; // To prevent caret overlapping