diff --git a/httpx/status_codes.py b/httpx/status_codes.py
index 5fe37299..557b7584 100644
--- a/httpx/status_codes.py
+++ b/httpx/status_codes.py
@@ -51,11 +51,11 @@ class StatusCode(IntEnum):
 
     @classmethod
     def is_client_error(cls, value: int) -> bool:
-        return value >= 400 and value <= 499
+        return 400 <= value <= 499
 
     @classmethod
     def is_server_error(cls, value: int) -> bool:
-        return value >= 500 and value <= 599
+        return 500 <= value <= 599
 
     # informational
     CONTINUE = 100, "Continue"