diff --git a/src/Microsoft.AspNet.Hosting/project.json b/src/Microsoft.AspNet.Hosting/project.json
index b2e9e33799..c5801b914d 100644
--- a/src/Microsoft.AspNet.Hosting/project.json
+++ b/src/Microsoft.AspNet.Hosting/project.json
@@ -33,7 +33,7 @@
     },
     "net451": {
       "frameworkAssemblies": {
-        "System.Runtime": ""
+        "System.Runtime": { "type": "build" }
       }
     },
     "dnxcore50": {