diff --git a/.changeset/sentry-client-entry.md b/.changeset/sentry-client-entry.md
new file mode 100644
index 000000000..8c4ef13f5
--- /dev/null
+++ b/.changeset/sentry-client-entry.md
@@ -0,0 +1,5 @@
+---
+"@workspace/web": patch
+---
+
+Sentry now initializes in a dedicated client entry before hydration, so client errors thrown during early module evaluation are captured. The router-aware browser-tracing integration is attached separately once the router exists.
diff --git a/apps/web/src/client.tsx b/apps/web/src/client.tsx
new file mode 100644
index 000000000..0e353b965
--- /dev/null
+++ b/apps/web/src/client.tsx
@@ -0,0 +1,30 @@
+import * as Sentry from "@sentry/tanstackstart-react";
+import { StartClient } from "@tanstack/react-start/client";
+import { StrictMode, startTransition } from "react";
+import { hydrateRoot } from "react-dom/client";
+
+// Initialize Sentry here, in the client entry, before hydration — so telemetry
+// emitted during module evaluation (e.g. a third-party lib that throws at import
+// time) is captured. The router-aware browser-tracing integration needs the
+// router instance, so it's attached separately in router.tsx via
+// Sentry.addIntegration once the router exists. See issue #320.
+//
+// The hydration below mirrors TanStack Start's default client entry for our
+// version; defining this file overrides that default.
+if (import.meta.env.VITE_SENTRY_DSN) {
+	Sentry.init({
+		dsn: import.meta.env.VITE_SENTRY_DSN,
+		environment: import.meta.env.MODE,
+		sendDefaultPii: true,
+		tracesSampleRate: 1.0,
+	});
+}
+
+startTransition(() => {
+	hydrateRoot(
+		document,
+		<StrictMode>
+			<StartClient />
+		</StrictMode>,
+	);
+});
diff --git a/apps/web/src/router.tsx b/apps/web/src/router.tsx
index 6a78883e5..683822cf8 100644
--- a/apps/web/src/router.tsx
+++ b/apps/web/src/router.tsx
@@ -26,14 +26,11 @@ export const getRouter = () => {
 		defaultStaleTime: 30_000, // Cache loader data for 30s to avoid re-fetching on navigations
 	});
 
+	// Sentry.init() runs in the client entry (client.tsx) before hydration; here
+	// we only attach the router-aware browser-tracing integration, which needs
+	// the router instance that doesn't exist yet at client-entry time. See #320.
 	if (!router.isServer && import.meta.env.VITE_SENTRY_DSN) {
-		Sentry.init({
-			dsn: import.meta.env.VITE_SENTRY_DSN,
-			environment: import.meta.env.MODE,
-			sendDefaultPii: true,
-			integrations: [Sentry.tanstackRouterBrowserTracingIntegration(router)],
-			tracesSampleRate: 1.0,
-		});
+		Sentry.addIntegration(Sentry.tanstackRouterBrowserTracingIntegration(router));
 	}
 
 	setupRouterSsrQueryIntegration({ router, queryClient: rqContext.queryClient });