diff --git a/singer_sdk/streams/rest.py b/singer_sdk/streams/rest.py
index 563956a5f..378b32c73 100644
--- a/singer_sdk/streams/rest.py
+++ b/singer_sdk/streams/rest.py
@@ -149,7 +149,7 @@ def requests_session(self) -> requests.Session:
     def validate_response(self, response: requests.Response) -> None:
         """Validate HTTP response.
 
-        Checks for error status codes and wether they are fatal or retriable.
+        Checks for error status codes and whether they are fatal or retriable.
 
         In case an error is deemed transient and can be safely retried, then this
         method should raise an :class:`singer_sdk.exceptions.RetriableAPIError`.
@@ -179,9 +179,7 @@ def validate_response(self, response: requests.Response) -> None:
         """
         if (
             response.status_code in self.extra_retry_statuses
-            or HTTPStatus.INTERNAL_SERVER_ERROR
-            <= response.status_code
-            <= max(HTTPStatus)
+            or response.status_code >= HTTPStatus.INTERNAL_SERVER_ERROR
         ):
             msg = self.response_error_message(response)
             raise RetriableAPIError(msg, response)
diff --git a/tests/core/rest/test_backoff.py b/tests/core/rest/test_backoff.py
index fbe391e55..7a2ba39b8 100644
--- a/tests/core/rest/test_backoff.py
+++ b/tests/core/rest/test_backoff.py
@@ -74,6 +74,14 @@ def custom_validation_stream(rest_tap):
                 match=r"503 Server Error: Service Unavailable for path: /dummy",
             ),
         ),
+        (
+            521,  # Cloudflare custom status code higher than max(HTTPStatus)
+            "Web Server Is Down",
+            pytest.raises(
+                RetriableAPIError,
+                match=r"521 Server Error: Web Server Is Down for path: /dummy",
+            ),
+        ),
         (
             429,
             "Too Many Requests",
@@ -84,7 +92,7 @@ def custom_validation_stream(rest_tap):
         ),
         (200, "OK", nullcontext()),
     ],
-    ids=["client-error", "server-error", "rate-limited", "ok"],
+    ids=["client-error", "server-error", "server-error", "rate-limited", "ok"],
 )
 def test_status_code_api(basic_rest_stream, status_code, reason, expectation):
     fake_response = requests.Response()