diff --git a/.changeset/shiny-olives-worry.md b/.changeset/shiny-olives-worry.md
new file mode 100644
index 00000000000..9f1c91d8c05
--- /dev/null
+++ b/.changeset/shiny-olives-worry.md
@@ -0,0 +1,5 @@
+---
+'@clerk/clerk-js': patch
+---
+
+Fix turnstile language fallback warning on captcha modal.
diff --git a/packages/clerk-js/src/ui/components/BlankCaptchaModal/index.tsx b/packages/clerk-js/src/ui/components/BlankCaptchaModal/index.tsx
index a1f35ba4b40..8cb936aa4f3 100644
--- a/packages/clerk-js/src/ui/components/BlankCaptchaModal/index.tsx
+++ b/packages/clerk-js/src/ui/components/BlankCaptchaModal/index.tsx
@@ -7,7 +7,9 @@ const BlankCard = withCardStateProvider(() => {
   const { locale } = useLocalizations();
   const captchaTheme = parsedCaptcha?.theme;
   const captchaSize = parsedCaptcha?.size;
-  const captchaLanguage = parsedCaptcha?.language || locale;
+  // Turnstile expects the language to be lowercase, so we convert it here (e.g. 'en-US' -> 'en-us')
+  // Supported languages: https://developers.cloudflare.com/turnstile/reference/supported-languages
+  const captchaLanguage = parsedCaptcha?.language || locale?.toLowerCase();
 
   return (
     <Card.Root>