diff --git a/src/Microsoft.AspNetCore.Http.Abstractions/project.json b/src/Microsoft.AspNetCore.Http.Abstractions/project.json
index 23f72dfaa3..4ae60ff733 100644
--- a/src/Microsoft.AspNetCore.Http.Abstractions/project.json
+++ b/src/Microsoft.AspNetCore.Http.Abstractions/project.json
@@ -24,8 +24,7 @@
   "frameworks": {
     "net451": {
       "frameworkAssemblies": {
-        "System.IO": "",
-        "System.Runtime": ""
+        "System.Runtime": { "type": "build" }
       }
     },
     "netstandard1.3": {
diff --git a/src/Microsoft.AspNetCore.WebUtilities/project.json b/src/Microsoft.AspNetCore.WebUtilities/project.json
index d186352ed5..235585b0d8 100644
--- a/src/Microsoft.AspNetCore.WebUtilities/project.json
+++ b/src/Microsoft.AspNetCore.WebUtilities/project.json
@@ -21,7 +21,7 @@
   "frameworks": {
     "net451": {
       "frameworkAssemblies": {
-        "System.Runtime": ""
+        "System.Runtime": { "type": "build" }
       }
     },
     "netstandard1.3": {