diff --git a/envoy/config/route/v3/route_components.proto b/envoy/config/route/v3/route_components.proto
index 46e7ae99..e4ad52e6 100644
--- a/envoy/config/route/v3/route_components.proto
+++ b/envoy/config/route/v3/route_components.proto
@@ -1490,6 +1490,10 @@ message RateLimit {
       // Metadata struct that defines the key and path to retrieve the string value. A match will
       // only happen if the value in the dynamic metadata is of type string.
       type.metadata.v3.MetadataKey metadata_key = 2 [(validate.rules).message = {required: true}];
+
+      // An optional value to use if *metadata_key* is empty. If not set and
+      // no value is present under the metadata_key then no descriptor is generated.
+      string default_value = 3;
     }
 
     oneof action_specifier {
diff --git a/envoy/config/route/v4alpha/route_components.proto b/envoy/config/route/v4alpha/route_components.proto
index 711914d9..01b138c7 100644
--- a/envoy/config/route/v4alpha/route_components.proto
+++ b/envoy/config/route/v4alpha/route_components.proto
@@ -1472,6 +1472,10 @@ message RateLimit {
       // Metadata struct that defines the key and path to retrieve the string value. A match will
       // only happen if the value in the dynamic metadata is of type string.
       type.metadata.v3.MetadataKey metadata_key = 2 [(validate.rules).message = {required: true}];
+
+      // An optional value to use if *metadata_key* is empty. If not set and
+      // no value is present under the metadata_key then no descriptor is generated.
+      string default_value = 3;
     }
 
     oneof action_specifier {