diff --git a/external/xamarin-android-tools b/external/xamarin-android-tools
index 9f02d77692b..47f95ab99f6 160000
--- a/external/xamarin-android-tools
+++ b/external/xamarin-android-tools
@@ -1 +1 @@
-Subproject commit 9f02d77692bca8c6585941de03750d5eaaca5c5a
+Subproject commit 47f95ab99f6201d956eecfa1c7b2fd5fa7e43946
diff --git a/src/Xamarin.Android.Build.Tasks/Tasks/AndroidDotnetToolTask.cs b/src/Xamarin.Android.Build.Tasks/Tasks/AndroidDotnetToolTask.cs
index efa01c48478..8f26c94f85c 100644
--- a/src/Xamarin.Android.Build.Tasks/Tasks/AndroidDotnetToolTask.cs
+++ b/src/Xamarin.Android.Build.Tasks/Tasks/AndroidDotnetToolTask.cs
@@ -105,7 +105,7 @@ string FindDotnet ()
 
 		string FindMono ()
 		{
-			string mono = BuildEngine4.GetRegisteredTaskObjectAssemblyLocal<string> (MonoKey, Lifetime);
+			string mono = BuildEngine4.GetRegisteredTaskObjectAssemblyLocal<string> (MonoKey, Lifetime, flags: RegisterTaskObjectKeyFlags.None);
 			if (!string.IsNullOrEmpty (mono)) {
 				Log.LogDebugMessage ($"Found cached mono via {nameof (BuildEngine4.RegisterTaskObject)}");
 				return mono;
@@ -116,7 +116,7 @@ string FindMono ()
 				foreach (var path in env.Split (Path.PathSeparator)) {
 					if (File.Exists (mono = Path.Combine (path, "mono"))) {
 						Log.LogDebugMessage ("Found mono in $PATH");
-						BuildEngine4.RegisterTaskObjectAssemblyLocal (MonoKey, mono, Lifetime);
+						BuildEngine4.RegisterTaskObjectAssemblyLocal (MonoKey, mono, Lifetime, flags: RegisterTaskObjectKeyFlags.None);
 						return mono;
 					}
 				}
@@ -125,13 +125,13 @@ string FindMono ()
 			foreach (var path in KnownMonoPaths) {
 				if (File.Exists (mono = path)) {
 					Log.LogDebugMessage ($"Found mono in {nameof (KnownMonoPaths)}");
-					BuildEngine4.RegisterTaskObjectAssemblyLocal (MonoKey, mono, Lifetime);
+					BuildEngine4.RegisterTaskObjectAssemblyLocal (MonoKey, mono, Lifetime, flags: RegisterTaskObjectKeyFlags.None);
 					return mono;
 				}
 			}
 
 			// Last resort
-			BuildEngine4.RegisterTaskObjectAssemblyLocal (MonoKey, mono = "mono", Lifetime);
+			BuildEngine4.RegisterTaskObjectAssemblyLocal (MonoKey, mono = "mono", Lifetime, flags: RegisterTaskObjectKeyFlags.None);
 			return mono;
 		}
 
diff --git a/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/IncrementalBuildTest.cs b/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/IncrementalBuildTest.cs
index 24fe06606b7..1c16ce4feb2 100644
--- a/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/IncrementalBuildTest.cs
+++ b/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/IncrementalBuildTest.cs
@@ -247,6 +247,30 @@ public void AllProjectsHaveSameOutputDirectory()
 			sb.Dispose ();
 		}
 
+		[Test]
+		public void BuildSolutionWithMultipleProjectsInParallel ()
+		{
+			var testPath = Path.Combine ("temp", "BuildSolutionWithMultipleProjects");
+			var sb = new SolutionBuilder("BuildSolutionWithMultipleProjects.sln") {
+				SolutionPath = Path.Combine (Root, testPath),
+				MaxCpuCount = 4,
+			};
+			for (int i=1; i <= 4; i++) {
+				var app1 = new XamarinAndroidApplicationProject () {
+					ProjectName = $"App{i}",
+					PackageName = $"com.companyname.App{i}",
+					AotAssemblies = true,
+					IsRelease = true,
+				};
+				app1.SetProperty ("AndroidEnableMarshalMethods", "True");
+				sb.Projects.Add (app1);
+			}
+			sb.BuildingInsideVisualStudio = false;
+			Assert.IsTrue (sb.Build (), "Build of solution should have succeeded");
+			Assert.IsTrue (sb.ReBuild (), "ReBuild of solution should have succeeded");
+			sb.Dispose ();
+		}
+
 		[Test]
 		public void JavacTaskDoesNotRunOnSecondBuild ()
 		{
diff --git a/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/Aapt2Tests.cs b/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/Aapt2Tests.cs
index 8ee83fc9876..dd2386b5d0e 100644
--- a/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/Aapt2Tests.cs
+++ b/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/Aapt2Tests.cs
@@ -105,7 +105,7 @@ public void Aapt2DaemonInstances (int maxInstances, int expectedMax, int expecte
 				DaemonKeepInDomain = false,
 			};
 			Assert.True (task.Execute (), $"task should have succeeded. {string.Join (";", errors.Select (x => x.Message))}");
-			var daemon = engine.GetRegisteredTaskObjectAssemblyLocal<Aapt2Daemon> (Aapt2Daemon.RegisterTaskObjectKey, RegisteredTaskObjectLifetime.Build);
+			var daemon = engine.GetRegisteredTaskObjectAssemblyLocal<Aapt2Daemon> (Aapt2Daemon.RegisterTaskObjectKey, RegisteredTaskObjectLifetime.Build, flags: RegisterTaskObjectKeyFlags.None);
 			Assert.IsNotNull (daemon, "Should have got a Daemon");
 			Assert.AreEqual (expectedMax, daemon.MaxInstances, $"Expected {expectedMax} but was {daemon.MaxInstances}");
 			Assert.AreEqual (expectedInstances, daemon.CurrentInstances, $"Expected {expectedInstances} but was {daemon.CurrentInstances}");
diff --git a/src/Xamarin.Android.Build.Tasks/Utilities/Aapt2Daemon.cs b/src/Xamarin.Android.Build.Tasks/Utilities/Aapt2Daemon.cs
index ec6aa25a035..db31d2b2252 100644
--- a/src/Xamarin.Android.Build.Tasks/Utilities/Aapt2Daemon.cs
+++ b/src/Xamarin.Android.Build.Tasks/Utilities/Aapt2Daemon.cs
@@ -22,11 +22,11 @@ internal class Aapt2Daemon : IDisposable
 		public static Aapt2Daemon GetInstance (IBuildEngine4 engine, string aapt2, int numberOfInstances, int initalNumberOfDaemons, bool registerInDomain = false)
 		{
 			var area = registerInDomain ? RegisteredTaskObjectLifetime.AppDomain : RegisteredTaskObjectLifetime.Build;
-			var daemon = engine.GetRegisteredTaskObjectAssemblyLocal<Aapt2Daemon> (RegisterTaskObjectKey, area);
+			var daemon = engine.GetRegisteredTaskObjectAssemblyLocal<Aapt2Daemon> (RegisterTaskObjectKey, area, flags: RegisterTaskObjectKeyFlags.None);
 			if (daemon == null)
 			{
 				daemon = new Aapt2Daemon (aapt2, numberOfInstances, initalNumberOfDaemons);
-				engine.RegisterTaskObjectAssemblyLocal (RegisterTaskObjectKey, daemon, area, allowEarlyCollection: false);
+				engine.RegisterTaskObjectAssemblyLocal (RegisterTaskObjectKey, daemon, area, allowEarlyCollection: false, flags: RegisterTaskObjectKeyFlags.None);
 			}
 			return daemon;
 		}