diff --git a/gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/client.py.j2 b/gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/client.py.j2
index 559fc72c1..9688ca750 100644
--- a/gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/client.py.j2
+++ b/gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/client.py.j2
@@ -186,7 +186,7 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
                 )
             else:
                 raise MutualTLSChannelError(
-                    "Unsupported GOOGLE_API_USE_MTLS value. Accepted values: Never, Auto, Always"
+                    "Unsupported GOOGLE_API_USE_MTLS value. Accepted values: never, auto, always"
                 )
 
         # Save or instantiate the transport.
diff --git a/gapic/templates/%namespace/%name_%version/%sub/services/%service/client.py.j2 b/gapic/templates/%namespace/%name_%version/%sub/services/%service/client.py.j2
index 16c3359d0..6e25957f6 100644
--- a/gapic/templates/%namespace/%name_%version/%sub/services/%service/client.py.j2
+++ b/gapic/templates/%namespace/%name_%version/%sub/services/%service/client.py.j2
@@ -186,7 +186,7 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
                 )
             else:
                 raise MutualTLSChannelError(
-                    "Unsupported GOOGLE_API_USE_MTLS value. Accepted values: Never, Auto, Always"
+                    "Unsupported GOOGLE_API_USE_MTLS value. Accepted values: never, auto, always"
                 )
 
         # Save or instantiate the transport.