diff --git a/src/System.Web.Http/Description/ApiDescription.cs b/src/System.Web.Http/Description/ApiDescription.cs
index b6f069b54..2e323fc14 100644
--- a/src/System.Web.Http/Description/ApiDescription.cs
+++ b/src/System.Web.Http/Description/ApiDescription.cs
@@ -22,6 +22,7 @@ public ApiDescription()
             SupportedRequestBodyFormatters = new Collection<MediaTypeFormatter>();
             SupportedResponseFormatters = new Collection<MediaTypeFormatter>();
             ParameterDescriptions = new Collection<ApiParameterDescription>();
+            ResponseDescription = new ResponseDescription();
         }
 
         /// <summary>