diff --git a/addons/web/static/src/legacy/js/fields/signature.js b/addons/web/static/src/legacy/js/fields/signature.js
index eadef64d4f5..fea26660a8c 100644
--- a/addons/web/static/src/legacy/js/fields/signature.js
+++ b/addons/web/static/src/legacy/js/fields/signature.js
@@ -45,10 +45,7 @@ var FieldBinarySignature = AbstractFieldBinary.extend({
      * @override
      */
     isSet: function () {
-        if (this.mode === 'edit') {
-            return this.value;
-        }
-        return true;
+        return this.value;
     },
 
     //--------------------------------------------------------------------------
diff --git a/addons/web/static/src/legacy/js/views/form/form_renderer.js b/addons/web/static/src/legacy/js/views/form/form_renderer.js
index 3608efe53b6..4c4a517f84c 100644
--- a/addons/web/static/src/legacy/js/views/form/form_renderer.js
+++ b/addons/web/static/src/legacy/js/views/form/form_renderer.js
@@ -46,6 +46,7 @@ var FormRenderer = BasicRenderer.extend({
         this.idsForLabels = {};
         this.lastActivatedFieldIndex = -1;
         this.alertFields = {};
+        this.labelsToPostProcess = [];
         // The form renderer doesn't render invsible fields (invisible="1") by
         // default, to speed up the rendering. However, we sometimes have to
         // display them (e.g. in Studio, in "show invisible" mode). This flag
@@ -170,6 +171,7 @@ var FormRenderer = BasicRenderer.extend({
             if (self.$('.o_field_invalid').length) {
                 self.canBeSaved(self.state.id);
             }
+            self._postProcessLabels();
             return resetWidgets;
         });
     },
@@ -461,6 +463,18 @@ var FormRenderer = BasicRenderer.extend({
             this.defaultFocusField = widget;
         }
     },
+    /**
+     * This function is called once form view is rendered or modifiers are
+     * changed to process labels to add o_form_label_empty.
+     *
+     * @private
+     */
+    _postProcessLabels() {
+        this.labelsToPostProcess.forEach((label) => {
+            label.call();
+        });
+        this.labelsToPostProcess = [];
+    },
     /**
      * @private
      * @param {Object} node
@@ -959,11 +973,12 @@ var FormRenderer = BasicRenderer.extend({
                 callback: function (element, modifiers, record) {
                     var widgets = self.allFieldWidgets[record.id];
                     var widget = _.findWhere(widgets, {name: fieldName});
+                    const fieldsInfo = record.fieldsInfo[self.viewType];
                     if (!widget) {
-                        return; // FIXME this occurs if the widget is created
-                                // after the label (explicit <label/> tag in the
-                                // arch), so this won't work on first rendering
-                                // only on reevaluation
+                        if (fieldsInfo[fieldName]) {
+                            self.labelsToPostProcess.push(element.callback.bind(self, element, modifiers, record));
+                        }
+                        return;
                     }
                     element.$el.toggleClass('o_form_label_empty', !!( // FIXME condition is evaluated twice (label AND widget...)
                         record.data.id
@@ -1090,6 +1105,7 @@ var FormRenderer = BasicRenderer.extend({
         delete this.defs;
 
         return Promise.all(defs).then(() => this.__renderView()).then(function () {
+            self._postProcessLabels();
             self._updateView($form.contents());
             if (self.state.res_id in self.alertFields) {
                 self.displayTranslationAlert();
diff --git a/addons/web/static/tests/legacy/views/form_tests.js b/addons/web/static/tests/legacy/views/form_tests.js
index 395b290b4c3..df4d8c00808 100644
--- a/addons/web/static/tests/legacy/views/form_tests.js
+++ b/addons/web/static/tests/legacy/views/form_tests.js
@@ -1543,6 +1543,65 @@ QUnit.module('Views', {
         form.destroy();
     });
 
+    QUnit.test('label tag added for fields have o_form_empty class in readonly mode if field is empty', async function (assert) {
+        assert.expect(8);
+
+        this.data.partner.fields.foo.default = false; // no default value for this test
+        this.data.partner.records[1].foo = false;  // 1 is record with id=2
+        this.data.partner.records[1].trululu = false;  // 1 is record with id=2
+        this.data.partner.fields.int_field.readonly = true;
+        this.data.partner.onchanges.foo = function (obj) {
+            if (obj.foo === "hello") {
+                obj.int_field = false;
+            }
+        };
+
+        const form = await createView({
+            View: FormView,
+            model: 'partner',
+            data: this.data,
+            arch: `<form string="Partners">
+                    <sheet>
+                        <label for="foo" string="Foo"/>
+                        <field name="foo"/>
+                        <label for="trululu" string="Trululu" attrs="{'readonly': [['foo', '=', False]]}"/>
+                        <field name="trululu" attrs="{'readonly': [['foo', '=', False]]}"/>
+                        <label for="int_field" string="IntField" attrs="{'readonly': [['int_field', '=', False]]}"/>
+                        <field name="int_field"/>
+                    </sheet>
+                </form>`,
+            res_id: 2,
+        });
+
+        assert.containsN(form, '.o_field_widget.o_field_empty', 2,
+            "should have 2 empty fields with correct class");
+        assert.containsN(form, '.o_form_label_empty', 2,
+            "should have 2 muted labels (for the empty fieds) in readonly");
+
+        await testUtils.form.clickEdit(form);
+
+        assert.containsOnce(form, '.o_field_empty',
+            "in edit mode, only empty readonly fields should have the o_field_empty class");
+        assert.containsOnce(form, '.o_form_label_empty',
+            "in edit mode, only labels associated to empty readonly fields should have the o_form_label_empty class");
+
+        await testUtils.fields.editInput(form.$('input[name=foo]'), 'test');
+
+        assert.containsNone(form, '.o_field_empty',
+            "after readonly modifier change, the o_field_empty class should have been removed");
+        assert.containsNone(form, '.o_form_label_empty',
+            "after readonly modifier change, the o_form_label_empty class should have been removed");
+
+        await testUtils.fields.editInput(form.$('input[name=foo]'), 'hello');
+
+        assert.containsOnce(form, '.o_field_empty',
+            "after value changed to false for a readonly field, the o_field_empty class should have been added");
+        assert.containsOnce(form, '.o_form_label_empty',
+            "after value changed to false for a readonly field, the o_form_label_empty class should have been added");
+
+        form.destroy();
+    });
+
     QUnit.test('form view can switch to edit mode', async function (assert) {
         assert.expect(9);