diff --git a/instrumentation-client.ts b/instrumentation-client.ts
index 57d4d0c..539beb5 100644
--- a/instrumentation-client.ts
+++ b/instrumentation-client.ts
@@ -11,7 +11,15 @@ posthog.init(process.env.NEXT_PUBLIC_POSTHOG_PROJECT_TOKEN!, {
   debug: process.env.NODE_ENV === 'development',
 });
 
-const sentryOptions = buildSentryOptions('client');
+// These must be written as literal `process.env.X` expressions: that is the
+// only form Next substitutes when building the client bundle. Reading them
+// dynamically leaves `undefined` in the browser and silently disables Sentry.
+const sentryOptions = buildSentryOptions('client', {
+  NEXT_PUBLIC_SENTRY_DSN: process.env.NEXT_PUBLIC_SENTRY_DSN,
+  NODE_ENV: process.env.NODE_ENV,
+  SENTRY_ENVIRONMENT: process.env.NEXT_PUBLIC_SENTRY_ENVIRONMENT,
+  SENTRY_RELEASE: process.env.NEXT_PUBLIC_SENTRY_RELEASE,
+});
 
 Sentry.init({
   enabled: sentryOptions.enabled,
diff --git a/tests/observability/client-dsn-inlining.test.ts b/tests/observability/client-dsn-inlining.test.ts
new file mode 100644
index 0000000..81f85e8
--- /dev/null
+++ b/tests/observability/client-dsn-inlining.test.ts
@@ -0,0 +1,28 @@
+import { readFileSync } from 'node:fs';
+import path from 'node:path';
+
+import { describe, expect, test } from 'vitest';
+
+/**
+ * Next only substitutes *literal* `process.env.NEXT_PUBLIC_*` references when
+ * it builds the client bundle. Reading the same name dynamically — say
+ * `env['NEXT_PUBLIC_SENTRY_DSN']` inside a helper — is left untouched, so the
+ * value is `undefined` in the browser and Sentry disables itself without any
+ * error. That shipped once already; these tests keep it from shipping again.
+ */
+describe('instrumentation-client.ts', () => {
+  const source = readFileSync(
+    path.resolve(__dirname, '../../instrumentation-client.ts'),
+    'utf8',
+  );
+
+  test('references the public DSN literally so the bundler can inline it', () => {
+    expect(source).toContain('process.env.NEXT_PUBLIC_SENTRY_DSN');
+  });
+
+  test('does not hand the raw process.env object to the options builder', () => {
+    // buildSentryOptions('client') with no second argument falls back to
+    // process.env, which is exactly the non-inlinable path.
+    expect(source).not.toMatch(/buildSentryOptions\(\s*'client'\s*\)/);
+  });
+});