diff --git a/content/520.md b/content/520.md
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+## Description
+
+<aside class="warning"><strong>Unofficial:</strong> This HTTP status code is not specified by any RFC.</aside>
+
+The HTTP response status code `520 Unknown Error` is an unofficial HTTP status code specific to [Cloudflare](https://cloudflare.com).
+
+This error occurs when the origin server returns an empty, unknown, or unexpected response to Cloudflare.
+
+### See Also
+
+- [Cloudflare Docs: Error 520](https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-520/)
diff --git a/lib/statuses.js b/lib/statuses.js
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--- a/lib/statuses.js
+++ b/lib/statuses.js
@@ -73,6 +73,7 @@ const statuses = {
   509: { code: 509, message: 'Bandwidth Limit Exceeded' },
   510: { code: 510, message: 'Not Extended' },
   511: { code: 511, message: 'Network Authentication Required' },
+  520: { code: 520, message: 'Cloudflare: Unknown Error' },
   521: { code: 521, message: 'Web Server Is Down' },
   522: { code: 522, message: 'Connection Timed Out' },
   523: { code: 523, message: 'Origin Is Unreachable' },
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