diff --git a/build/Targets/Imports.targets b/build/Targets/Imports.targets
index 1f010ff9198702b562f17fb9a511911cb5b55574..4b16a9b941bc314a4e5eef4020b7946d4983e752 100644
--- a/build/Targets/Imports.targets
+++ b/build/Targets/Imports.targets
@@ -353,7 +353,7 @@
              Condition="!Exists('$(ToolsetCompilerPropsFilePath)')" />
   </Target>
 
-  <Target Name="CheckBootstrapState" Condition="'$(BootstrapBuildPath)' != ''" BeforeTargets="CoreCompile">
+  <Target Name="CheckBootstrapState" Condition="'$(BootstrapBuildPath)' != ''" AfterTargets="CoreCompile">
     <ValidateBootstrap BootstrapPath="$(BootstrapBuildPath)" />
   </Target>
 
diff --git a/src/Compilers/Core/MSBuildTask/AssemblyResolution.cs b/src/Compilers/Core/MSBuildTask/AssemblyResolution.cs
index 1951262e4fea75f65c4e4a8597b5fd77f2c88efe..88a011d4a80bf5e63a6b819504b5e04483f5602e 100644
--- a/src/Compilers/Core/MSBuildTask/AssemblyResolution.cs
+++ b/src/Compilers/Core/MSBuildTask/AssemblyResolution.cs
@@ -54,10 +54,15 @@ private static bool TryRedirect(AssemblyName name)
                     return TryRedirect(name, s_b03f5f7f11d50a3a, 4, 0, 2, 0);
 
                 case "System.Diagnostics.StackTrace":
+                case "System.Security.AccessControl":
                     return TryRedirect(name, s_b03f5f7f11d50a3a, 4, 0, 3, 0);
 
             }
 
+#if DEBUG || BOOTSTRAP
+            ValidateBootstrap.AddFailedLoad(name);
+#endif
+
             return false;
         }
 
diff --git a/src/Compilers/Core/MSBuildTask/ValidateBootstrap.cs b/src/Compilers/Core/MSBuildTask/ValidateBootstrap.cs
index 1379efa5b01b323b74979acedf47a48b5f516f1c..ead4e9a0b3f2f4292fba60261b663535120554df 100644
--- a/src/Compilers/Core/MSBuildTask/ValidateBootstrap.cs
+++ b/src/Compilers/Core/MSBuildTask/ValidateBootstrap.cs
@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using Microsoft.Build.Utilities;
+using System.Collections.Concurrent;
 using System.IO;
+using System.Linq;
 using System.Reflection;
 using System;
 
@@ -15,6 +17,8 @@ namespace Microsoft.CodeAnalysis.BuildTasks
     /// </summary>
     public sealed class ValidateBootstrap : Task
     {
+        private static readonly ConcurrentDictionary<AssemblyName, byte> s_failedLoadSet = new ConcurrentDictionary<AssemblyName, byte>();
+
         private string _bootstrapPath;
 
         public string BootstrapPath
@@ -26,6 +30,7 @@ public string BootstrapPath
         public ValidateBootstrap()
         {
 
+
         }
 
         public override bool Execute()
@@ -54,6 +59,16 @@ public override bool Execute()
                 }
             }
 
+            var failedLoads = s_failedLoadSet.Keys.ToList();
+            if (failedLoads.Count > 0)
+            {
+                foreach (var name in failedLoads.OrderBy(x => x.Name))
+                {
+                    Log.LogError($"Assembly resolution failed for {name}");
+                    allGood = false;
+                }
+            }
+
             return allGood;
         }
 
@@ -74,6 +89,21 @@ private static string NormalizePath(string path)
         }
 
         private string GetDirectory(Assembly assembly) => Path.GetDirectoryName(Utilities.GetLocation(assembly));
+
+        internal static void AddFailedLoad(AssemblyName name)
+        {
+            switch (name.Name)
+            {
+                case "System":
+                case "System.Core":
+                case "Microsoft.Build.Tasks.CodeAnalysis.resources":
+                    // These are failures are expected by design.
+                    break;
+                default:
+                    s_failedLoadSet.TryAdd(name, 0);
+                    break;
+            }
+        }
     }
 #endif
 }
diff --git a/src/Compilers/Core/MSBuildTask/project.json b/src/Compilers/Core/MSBuildTask/project.json
index 695676191007fe767fec1684786e29e6ad9f1bed..66b6c6a624968faa6665ed7cd239015b3f4dc160 100644
--- a/src/Compilers/Core/MSBuildTask/project.json
+++ b/src/Compilers/Core/MSBuildTask/project.json
@@ -7,6 +7,7 @@
         "Microsoft.Win32.Primitives": "4.3.0",
         "System.AppContext": "4.3.0",
         "System.Console": "4.3.0",
+        "System.Collections.Concurrent": "4.3.0",
         "System.Diagnostics.Process": "4.3.0",
         "System.Diagnostics.Tools": "4.3.0",
         "System.IO.FileSystem": "4.3.0",
@@ -31,4 +32,4 @@
             ]
         }
     }
-}
\ No newline at end of file
+}