diff --git a/Documentation/docs-mobile/messages/xa1042.md b/Documentation/docs-mobile/messages/xa1042.md
new file mode 100644
index 00000000000..f57c6e6cbd2
--- /dev/null
+++ b/Documentation/docs-mobile/messages/xa1042.md
@@ -0,0 +1,45 @@
+---
+title: .NET for Android warning XA1042
+description: XA1042 warning code
+ms.date: 04/02/2026
+f1_keywords:
+ - "XA1042"
+---
+
+# .NET for Android warning XA1042
+
+## Example messages
+
+```
+warning XA1042: The MSBuild property 'RunAOTCompilation' is not compatible with the CoreCLR runtime and will be ignored. Either remove the property or guard it with a condition: Condition="'$(UseMonoRuntime)' == 'true'"
+```
+
+## Issue
+
+This warning indicates that a Mono-specific MSBuild property is set in
+the project file, but the project is configured to use a non-Mono
+runtime (such as CoreCLR or NativeAOT). The property will have no
+effect with the current runtime and will be ignored.
+
+Properties that trigger this warning include:
+- `RunAOTCompilation` — Mono AOT compilation; CoreCLR uses `PublishReadyToRun` instead.
+- `EnableLLVM` — Enables LLVM for the Mono AOT compiler.
+
+## Solution
+
+Remove the Mono-specific property from your project file or
+`Directory.Build.props`, or guard it with a runtime condition:
+
+```xml
+
+ true
+
+```
+
+For CoreCLR, use `PublishReadyToRun` instead of `RunAOTCompilation`:
+
+```xml
+
+ true
+
+```
diff --git a/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.Aot.targets b/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.Aot.targets
index d80be84d01c..3537c75fb4b 100644
--- a/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.Aot.targets
+++ b/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.Aot.targets
@@ -21,7 +21,7 @@ They run in a context of an inner build with a single $(RuntimeIdentifier).
when $(MonoAOTCompilerTasksAssemblyPath) is blank:
https://github.com/dotnet/runtime/blob/69711860262e44458bbe276393ea3eb9f7a2192a/src/mono/nuget/Microsoft.NET.Workload.Mono.Toolchain.Manifest/WorkloadManifest.targets.in#L20-L25
-->
-
+
@@ -39,7 +39,7 @@ They run in a context of an inner build with a single $(RuntimeIdentifier).
diff --git a/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets b/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets
index e9c75e1667d..fd8c19234f1 100644
--- a/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets
+++ b/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets
@@ -119,6 +119,11 @@
true
true
false
+
+ <_AndroidXA1042_RunAOTCompilation Condition=" '$(RunAOTCompilation)' == 'true' and '$(_AndroidRuntime)' != 'MonoVM' ">true
+ <_AndroidXA1042_EnableLLVM Condition=" '$(EnableLLVM)' == 'true' and '$(_AndroidRuntime)' != 'MonoVM' ">true
+ false
+ false
<_AndroidXA1029 Condition=" '$(AotAssemblies)' != '' ">true
<_AndroidXA1030 Condition=" '$(RunAOTCompilation)' == 'true' and '$(PublishTrimmed)' == 'false' ">true
$(RunAOTCompilation)
diff --git a/src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs b/src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs
index bc2d9a7d4d4..4b7c0de91fc 100644
--- a/src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs
+++ b/src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs
@@ -938,6 +938,15 @@ public static string XA1041 {
}
}
+ ///
+ /// Looks up a localized string similar to The MSBuild property '{0}' is not compatible with the {1} runtime and will be ignored. Either remove the property or guard it with a condition: Condition="'$(UseMonoRuntime)' == 'true'".
+ ///
+ public static string XA1042 {
+ get {
+ return ResourceManager.GetString("XA1042", resourceCulture);
+ }
+ }
+
///
/// Looks up a localized string similar to Use of AppDomain.CreateDomain() detected in assembly: {0}. .NET 6 and higher will only support a single AppDomain, so this API will no longer be available in .NET for Android once .NET 6 is released..
///
diff --git a/src/Xamarin.Android.Build.Tasks/Properties/Resources.resx b/src/Xamarin.Android.Build.Tasks/Properties/Resources.resx
index d1ee02dc051..6d6eb3546f6 100644
--- a/src/Xamarin.Android.Build.Tasks/Properties/Resources.resx
+++ b/src/Xamarin.Android.Build.Tasks/Properties/Resources.resx
@@ -1007,6 +1007,13 @@ To use a custom JDK path for a command line build, set the 'JavaSdkDirectory' MS
The following are literal names and should not be translated: .NET.
{0} - The MSBuild property that has the incorrect value.
{1} - The current value of the property
+
+
+
+ The MSBuild property '{0}' is not compatible with the {1} runtime and will be ignored. Either remove the property or guard it with a condition: Condition="'$(UseMonoRuntime)' == 'true'"
+ The following are literal names and should not be translated: MSBuild, UseMonoRuntime.
+{0} - The MSBuild property name (e.g. RunAOTCompilation, EnableLLVM).
+{1} - The name of the .NET runtime (e.g. CoreCLR, NativeAOT).
diff --git a/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AotTests.cs b/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AotTests.cs
index 6a6b91aa900..09d36e7b02a 100644
--- a/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AotTests.cs
+++ b/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AotTests.cs
@@ -492,5 +492,37 @@ public void CheckWhetherLibcAndLibmAreReferencedInAOTLibraries ()
}
}
+ [Test]
+ public void RunAOTCompilationWithCoreClrWarnsAndSkipsMonoAot ()
+ {
+ var proj = new XamarinAndroidApplicationProject {
+ IsRelease = true,
+ };
+ proj.SetRuntime (AndroidRuntime.CoreCLR);
+ proj.SetProperty ("RunAOTCompilation", "true");
+
+ using var b = CreateApkBuilder ();
+ Assert.IsTrue (b.Build (proj), "Build should have succeeded.");
+ StringAssertEx.Contains ("warning XA1042", b.LastBuildOutput, "Build output should contain warning XA1042");
+ StringAssertEx.Contains ("RunAOTCompilation", b.LastBuildOutput, "Build output should mention RunAOTCompilation");
+ StringAssertEx.Contains ("CoreCLR", b.LastBuildOutput, "Build output should mention CoreCLR");
+ }
+
+ [Test]
+ public void EnableLLVMWithCoreClrWarnsAndIsIgnored ()
+ {
+ var proj = new XamarinAndroidApplicationProject {
+ IsRelease = true,
+ };
+ proj.SetRuntime (AndroidRuntime.CoreCLR);
+ proj.SetProperty ("EnableLLVM", "true");
+
+ using var b = CreateApkBuilder ();
+ Assert.IsTrue (b.Build (proj), "Build should have succeeded.");
+ StringAssertEx.Contains ("warning XA1042", b.LastBuildOutput, "Build output should contain warning XA1042");
+ StringAssertEx.Contains ("EnableLLVM", b.LastBuildOutput, "Build output should mention EnableLLVM");
+ StringAssertEx.Contains ("CoreCLR", b.LastBuildOutput, "Build output should mention CoreCLR");
+ }
+
}
}
diff --git a/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets b/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
index c2527d1954e..e6a46aab923 100644
--- a/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
+++ b/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
@@ -550,6 +550,16 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
ResourceName="XA1030"
Condition=" $(_AndroidXA1030) == 'true' "
/>
+
+