diff --git a/src/vaadin-time-picker.html b/src/vaadin-time-picker.html
index 3c51d3a..65d24b0 100644
--- a/src/vaadin-time-picker.html
+++ b/src/vaadin-time-picker.html
@@ -218,7 +218,8 @@
              */
             readonly: {
               type: Boolean,
-              value: false
+              value: false,
+              reflectToAttribute: true
             },
 
             /**
diff --git a/test/input-test.html b/test/input-test.html
index 564bbf3..ea74075 100644
--- a/test/input-test.html
+++ b/test/input-test.html
@@ -205,6 +205,11 @@
           });
         });
 
+        it('should reflect to attribute when readonly property is set', () => {
+          timePicker.readonly = true;
+          expect(timePicker.hasAttribute('readonly')).to.be.true;
+        });
+
         describe('aria', () => {
           it('text-field should have the `aria-label` attribute', () => {
             expect(timePicker.__inputElement.hasAttribute('aria-label')).to.be.false;