diff --git a/ghost/portal/src/components/PopupModal.js b/ghost/portal/src/components/PopupModal.js
index edc95abaa1..89c5f559df 100644
--- a/ghost/portal/src/components/PopupModal.js
+++ b/ghost/portal/src/components/PopupModal.js
@@ -10,7 +10,7 @@ const React = require('react');
 const StylesWrapper = ({member}) => {
     return {
         modalContainer: {
-            zIndex: '1000',
+            zIndex: '3999999',
             position: 'fixed',
             left: '0',
             top: '0',
@@ -153,6 +153,9 @@ export default class PopupModal extends React.Component {
         const frameStyle = {
             ...Styles.frame.common
         };
+        if (hasMode(['preview', 'dev'])) {
+            Styles.modalContainer.zIndex = '3999997';
+        }
         return (
             <div style={Styles.modalContainer}>
                 <Frame style={frameStyle} title="membersjs-popup" head={this.renderFrameStyles()}>
diff --git a/ghost/portal/src/components/TriggerButton.js b/ghost/portal/src/components/TriggerButton.js
index a6d0ca6c04..5ae3ba4178 100644
--- a/ghost/portal/src/components/TriggerButton.js
+++ b/ghost/portal/src/components/TriggerButton.js
@@ -28,7 +28,7 @@ const Styles = ({brandColor, hasText}) => {
     const invertColor = getContrastColor(brandColor);
     return {
         frame: {
-            zIndex: '2147483000',
+            zIndex: '3999998',
             position: 'fixed',
             bottom: '28px',
             right: '28px',