diff --git a/app/src/components/Theme.test.js b/app/src/components/Theme.test.js
index 1c76ea88..8389e509 100644
--- a/app/src/components/Theme.test.js
+++ b/app/src/components/Theme.test.js
@@ -1,5 +1,5 @@
 import React from 'react';
-import {Progress} from './Theme';
+import {Button, Modal, Progress} from './Theme';
 import {renderInDarkMode, renderInLightMode} from '../test-utils';
 
 // All semantic-ui colors.
@@ -10,6 +10,34 @@ const lightBarColors = ['yellow', 'olive', 'teal'];
 // Bar colors that need dark percent text only in dark mode (inverted makes bar lighter).
 const darkModeLightBarColors = ['grey', 'blue'];
 
+describe('Button ref forwarding', () => {
+    // Regression: SButton is a class component, so forwarding a ref straight to it resolves to the class instance
+    // (no `.contains`). Semantic UI's Modal/Popup Portal calls `node.contains(...)` on the trigger's ref during
+    // handleDocumentClick, throwing "node.contains is not a function". The forwarded ref must be the DOM <button>.
+    it('resolves a forwarded ref to the underlying DOM element', () => {
+        const ref = React.createRef();
+        renderInLightMode(<Button ref={ref} content='Click'/>);
+
+        expect(ref.current).toBeInstanceOf(HTMLElement);
+        expect(typeof ref.current.contains).toBe('function');
+        expect(ref.current.tagName).toBe('BUTTON');
+    });
+
+    it('does not throw when a Button is used as a controlled Modal trigger and the document is clicked', () => {
+        // Reproduces the Control page crash: an open Modal whose trigger is a themed Button. A document click
+        // invokes the Portal's handleDocumentClick -> doesNodeContainClick(triggerRef.current, e).
+        renderInLightMode(
+            <Modal open trigger={<Button content='Open'/>}>
+                <Modal.Content>content</Modal.Content>
+            </Modal>
+        );
+
+        expect(() => {
+            document.body.dispatchEvent(new MouseEvent('click', {bubbles: true}));
+        }).not.toThrow();
+    });
+});
+
 describe('Progress component theme support', () => {
     describe('dark mode', () => {
         it('adds inverted-progress-text class for label readability', () => {
diff --git a/app/src/components/Theme.tsx b/app/src/components/Theme.tsx
index 023ec090..dd71446f 100644
--- a/app/src/components/Theme.tsx
+++ b/app/src/components/Theme.tsx
@@ -34,6 +34,7 @@ import {
     Placeholder as SPlaceholder,
     Popup as SPopup,
     Progress as SProgress,
+    Ref as SRef,
     Segment as SSegment,
     Statistic as SStatistic,
     StatisticGroup as SStatisticGroup,
@@ -287,7 +288,13 @@ const ButtonGroup: ButtonGroupComponent = (props) => {
 const ButtonBase = forwardRef<any, ButtonProps>((props, ref) => {
     const {i, inverted} = useContext(ThemeContext);
     const mergedProps = defaultGrey({...i, ...props}, !!inverted);
-    return <SButton ref={ref} {...mergedProps}/>
+    // SButton is a class component, so a forwarded `ref` would resolve to the class instance rather than the DOM
+    // node. Semantic UI's Modal/Popup use the trigger's ref with `node.contains(...)`, which throws on a non-DOM
+    // value. Wrap in Ref (findDOMNode) so the forwarded ref always resolves to the underlying <button> element.
+    if (ref) {
+        return <SRef innerRef={ref}><SButton {...mergedProps}/></SRef>
+    }
+    return <SButton {...mergedProps}/>
 });
 ButtonBase.displayName = 'ButtonBase';