diff --git a/.changeset/fix-ui-captcha-inert-boolean.md b/.changeset/fix-ui-captcha-inert-boolean.md
new file mode 100644
index 00000000000..ce5ebc6061a
--- /dev/null
+++ b/.changeset/fix-ui-captcha-inert-boolean.md
@@ -0,0 +1,5 @@
+---
+'@clerk/ui': patch
+---
+
+Use a React 19-safe boolean `inert` value when the sign-in or sign-up captcha becomes interactive, so the form is actually inert and the empty-string warning is gone.
diff --git a/packages/ui/src/components/SignIn/SignInStart.tsx b/packages/ui/src/components/SignIn/SignInStart.tsx
index d2115a3e575..71b14ab903b 100644
--- a/packages/ui/src/components/SignIn/SignInStart.tsx
+++ b/packages/ui/src/components/SignIn/SignInStart.tsx
@@ -1,4 +1,5 @@
 import { getAlternativePhoneCodeProviderData } from '@clerk/shared/alternativePhoneCode';
+import { inertProps } from '@clerk/shared/inert';
 import { ERROR_CODES, SIGN_UP_MODES } from '@clerk/shared/internal/clerk-js/constants';
 import { clerkInvalidFAPIResponse } from '@clerk/shared/internal/clerk-js/errors';
 import { getClerkQueryParam, removeClerkQueryParam } from '@clerk/shared/internal/clerk-js/queryParams';
@@ -644,8 +645,7 @@ function SignInStartInternal(): JSX.Element {
             <Col
               elementDescriptor={descriptors.main}
               gap={6}
-              // @ts-ignore - `inert` is not yet in the installed React types
-              inert={captchaIsInteractive ? '' : undefined}
+              {...inertProps(captchaIsInteractive)}
               // `display:none` (not `visibility:hidden`) so the collapsed column leaves flex flow and
               // contributes no `gap` gutter to `Card.Content` — otherwise it injects empty space above
               // the spotlighted captcha. Subtree stays mounted (form state preserved); `inert` is then
diff --git a/packages/ui/src/components/SignUp/SignUpStart.tsx b/packages/ui/src/components/SignUp/SignUpStart.tsx
index e565ea575f3..579e0c22f5d 100644
--- a/packages/ui/src/components/SignUp/SignUpStart.tsx
+++ b/packages/ui/src/components/SignUp/SignUpStart.tsx
@@ -1,5 +1,6 @@
 import { getAlternativePhoneCodeProviderData } from '@clerk/shared/alternativePhoneCode';
 import { isClerkAPIResponseError } from '@clerk/shared/error';
+import { inertProps } from '@clerk/shared/inert';
 import { ERROR_CODES, SIGN_UP_MODES } from '@clerk/shared/internal/clerk-js/constants';
 import { getClerkQueryParam } from '@clerk/shared/internal/clerk-js/queryParams';
 import { useClerk } from '@clerk/shared/react';
@@ -421,8 +422,7 @@ function SignUpStartInternal(): JSX.Element {
               direction='col'
               elementDescriptor={descriptors.main}
               gap={6}
-              // @ts-ignore - `inert` is not yet in the installed React types
-              inert={captchaIsInteractive ? '' : undefined}
+              {...inertProps(captchaIsInteractive)}
               // `display:none` (not `visibility:hidden`) so the collapsed column leaves flex flow and
               // contributes no `gap` gutter to `Card.Content` — otherwise it injects empty space above
               // the spotlighted captcha. Subtree stays mounted (form state preserved); `inert` is then