diff --git a/src/Microsoft.AspNet.WebSockets.Protocol/project.json b/src/Microsoft.AspNet.WebSockets.Protocol/project.json
index 3bf854488d..296af96c55 100644
--- a/src/Microsoft.AspNet.WebSockets.Protocol/project.json
+++ b/src/Microsoft.AspNet.WebSockets.Protocol/project.json
@@ -6,6 +6,7 @@
             "dependencies": {
                 "Microsoft.Net.WebSocketAbstractions": "1.0.0-*",
                 "System.Diagnostics.Contracts": "4.0.0-beta-*",
+                "System.IO": "4.0.10-beta-*",
                 "System.Linq": "4.0.0-beta-*",
                 "System.Runtime": "4.0.20-beta-*",
                 "System.Runtime.InteropServices": "4.0.20-beta-*",