diff --git a/src/mono/wasm/Wasm.Build.Tests/NativeRebuildTests/ReferenceNewAssemblyRebuildTest.cs b/src/mono/wasm/Wasm.Build.Tests/NativeRebuildTests/ReferenceNewAssemblyRebuildTest.cs
index e1620d2dd77101..15f33923a1b8a4 100644
--- a/src/mono/wasm/Wasm.Build.Tests/NativeRebuildTests/ReferenceNewAssemblyRebuildTest.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/NativeRebuildTests/ReferenceNewAssemblyRebuildTest.cs
@@ -25,7 +25,13 @@ public ReferenceNewAssemblyRebuildTest(ITestOutputHelper output, SharedBuildPerT
         [MemberData(nameof(NativeBuildData))]
         public async Task ReferenceNewAssembly(Configuration config, bool aot, bool nativeRelink, bool invariant)
         {
-            ProjectInfo info = CopyTestAsset(config, aot, TestAsset.WasmBasicTestApp, "rebuild_tasks");     
+            // Reference a dedicated first-party library that the default app does not use, so it is
+            // trimmed away on the first build and only enters the AOT module set once the swapped
+            // entry point references it. Relying on a specific BCL assembly being absent from the
+            // closure is fragile (it has silently regressed as the base app's dependencies grew).
+            string extraItems = @"<ProjectReference Include=""..\Library\Library.csproj"" />";
+            ProjectInfo info = CopyTestAsset(config, aot, TestAsset.WasmBasicTestApp, "rebuild_tasks", extraItems: extraItems);
+            ReplaceFile(Path.Combine("..", "Library", "Library.cs"), Path.Combine(BuildEnvironment.TestAssetsPath, "EntryPoints", "NativeRebuildReferencedLibrary.cs"));
             BuildPaths paths = await FirstNativeBuildAndRun(info, config, aot, nativeRelink, invariant);
 
             var pathsDict = GetFilesTable(info.ProjectName, aot, paths, unchanged: false);
diff --git a/src/mono/wasm/testassets/EntryPoints/NativeRebuildNewAssembly.cs b/src/mono/wasm/testassets/EntryPoints/NativeRebuildNewAssembly.cs
index bff7ffb3827a40..f870ba88b7f828 100644
--- a/src/mono/wasm/testassets/EntryPoints/NativeRebuildNewAssembly.cs
+++ b/src/mono/wasm/testassets/EntryPoints/NativeRebuildNewAssembly.cs
@@ -1,17 +1,10 @@
-using System;
-using System.Security.Cryptography;
-using System.Text;
+// Reference a dedicated first-party library ("Library") that is not part of
+// the WasmBasicTestApp's default assembly closure. This guarantees the rebuild
+// pulls in a genuinely new AOT module, regardless of which BCL assemblies the
+// base app happens to root.
+using NativeRebuildReferencedLibrary;
+
 public class Test
 {
-    public static int Main()
-    {
-        string input = "Hello, world!";
-        using (SHA256 sha256 = SHA256.Create())
-        {
-            byte[] inputBytes = Encoding.UTF8.GetBytes(input);
-            byte[] hashBytes = sha256.ComputeHash(inputBytes);
-            Console.WriteLine($"Hash of {input}: {Convert.ToBase64String(hashBytes)}");
-        }
-        return 42;
-    }
+    public static int Main() => NewlyReferencedType.GetValue();
 }
diff --git a/src/mono/wasm/testassets/EntryPoints/NativeRebuildReferencedLibrary.cs b/src/mono/wasm/testassets/EntryPoints/NativeRebuildReferencedLibrary.cs
new file mode 100644
index 00000000000000..9d2c0ed0d0ba6c
--- /dev/null
+++ b/src/mono/wasm/testassets/EntryPoints/NativeRebuildReferencedLibrary.cs
@@ -0,0 +1,6 @@
+namespace NativeRebuildReferencedLibrary;
+
+public static class NewlyReferencedType
+{
+    public static int GetValue() => 42;
+}