diff --git a/src/core/primitives/Dialog/fragments/DialogPrimitivePortal.tsx b/src/core/primitives/Dialog/fragments/DialogPrimitivePortal.tsx
index b557df262..fddade5fc 100644
--- a/src/core/primitives/Dialog/fragments/DialogPrimitivePortal.tsx
+++ b/src/core/primitives/Dialog/fragments/DialogPrimitivePortal.tsx
@@ -22,22 +22,16 @@ const DialogPrimitivePortal = ({
     const [isMounted, setIsMounted] = useState(false);
 
     useEffect(() => {
-        // Only run on client side after component mounts
         if (container) {
             rootElementRef.current = container as HTMLElement;
         } else {
-            const themeContainer = themeContext?.portalRootRef.current
-                || document.querySelector('[data-rad-ui-portal-root]') as HTMLElement | null
-                || themeContext?.containerRef.current
-                || document.querySelector('#rad-ui-theme-container') as HTMLElement | null;
-            const fallback = document.body;
-            const selectedRoot = themeContainer || fallback;
-            rootElementRef.current = selectedRoot;
+            rootElementRef.current = themeContext?.portalRootRef.current
+                ?? themeContext?.containerRef.current
+                ?? document.body;
         }
         setIsMounted(true);
     }, [container, themeContext]);
 
-    // Don't render anything until mounted (SSR safety)
     if (!isMounted) {
         return null;
     }
diff --git a/src/core/primitives/Dialog/tests/DialogPrimitive.portal.test.tsx b/src/core/primitives/Dialog/tests/DialogPrimitive.portal.test.tsx
new file mode 100644
index 000000000..599f1a6a9
--- /dev/null
+++ b/src/core/primitives/Dialog/tests/DialogPrimitive.portal.test.tsx
@@ -0,0 +1,28 @@
+import React from 'react';
+import { render, screen } from '@testing-library/react';
+import ThemeContext from '~/components/ui/Theme/ThemeContext';
+import DialogPrimitive from '~/core/primitives/Dialog';
+
+describe('Dialog primitive portal', () => {
+    test('portals into Theme portalRootRef when provided', () => {
+        const portalRoot = document.createElement('div');
+        document.body.appendChild(portalRoot);
+
+        render(
+            <ThemeContext.Provider
+                value={{
+                    containerRef: { current: null },
+                    portalRootRef: { current: portalRoot }
+                }}>
+                <DialogPrimitive.Root open>
+                    <DialogPrimitive.Portal>
+                        <DialogPrimitive.Content>Dialog body</DialogPrimitive.Content>
+                    </DialogPrimitive.Portal>
+                </DialogPrimitive.Root>
+            </ThemeContext.Provider>
+        );
+
+        expect(portalRoot).toContainElement(screen.getByText('Dialog body'));
+        portalRoot.remove();
+    });
+});
diff --git a/src/test-utils/portal.ts b/src/test-utils/portal.ts
index 5a2de265d..b2362178d 100644
--- a/src/test-utils/portal.ts
+++ b/src/test-utils/portal.ts
@@ -1,17 +1,37 @@
+import React from 'react';
 import { render } from '@testing-library/react';
 import userEvent from '@testing-library/user-event';
+import ThemeContext from '~/components/ui/Theme/ThemeContext';
 
 export function renderWithPortal(ui: React.ReactElement) {
     const portalRoot = document.createElement('div');
-    portalRoot.setAttribute('id', 'rad-ui-theme-container');
+    portalRoot.setAttribute('data-rad-ui-portal-root', '');
     document.body.appendChild(portalRoot);
-    const result = render(ui);
+
+    const themeContainer = document.createElement('div');
+    themeContainer.setAttribute('id', 'rad-ui-theme-container');
+    document.body.appendChild(themeContainer);
+
+    const result = render(
+        React.createElement(
+            ThemeContext.Provider,
+            {
+                value: {
+                    containerRef: { current: themeContainer },
+                    portalRootRef: { current: portalRoot }
+                }
+            },
+            ui
+        )
+    );
+
     return {
         ...result,
         portalRoot,
         cleanup: () => {
             result.unmount();
             portalRoot.remove();
+            themeContainer.remove();
         }
     };
 }
@@ -28,7 +48,6 @@ export async function assertFocusTrap(container: HTMLElement) {
     }
     const first = focusable[0];
     const last = focusable[focusable.length - 1];
-    // TODO: track jsdom focus trap flakiness and re-enable assertions in CI when stable.
     const isJsdom = typeof navigator !== 'undefined' && /jsdom/i.test(navigator.userAgent);
 
     first.focus();