diff --git a/src/service_identity/exceptions.py b/src/service_identity/exceptions.py
index 5d573f6..a0c6f29 100644
--- a/src/service_identity/exceptions.py
+++ b/src/service_identity/exceptions.py
@@ -72,6 +72,9 @@ def __str__(self) -> str:
 
 
 class CertificateError(Exception):
-    """
+    r"""
     Certificate contains invalid or unexpected data.
+
+    This includes the case where s certificate contains no
+    ``subjectAltName``\ s.
     """