diff --git a/google/protobuf/descriptor.proto b/google/protobuf/descriptor.proto
index 801d85e44624f..c59a6022e717d 100644
--- a/google/protobuf/descriptor.proto
+++ b/google/protobuf/descriptor.proto
@@ -43,8 +43,7 @@ package google.protobuf;
 option go_package = "descriptor";
 option java_package = "com.google.protobuf";
 option java_outer_classname = "DescriptorProtos";
-// Re-enable this once the tools have picked up the csharp_namespace option.
-// option csharp_namespace = "Google.ProtocolBuffers.DescriptorProtos";
+option csharp_namespace = "Google.Protobuf.Reflection";
 option objc_class_prefix = "GPB";
 
 // descriptor.proto must be optimized for speed because reflection-based