diff --git a/tests/Beam/Fable.Tests.Beam.fsproj b/tests/Beam/Fable.Tests.Beam.fsproj
index 19bed181ad..525cda2c1d 100644
--- a/tests/Beam/Fable.Tests.Beam.fsproj
+++ b/tests/Beam/Fable.Tests.Beam.fsproj
@@ -1,6 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
+    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
+         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
+         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+    <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
+    <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -10,7 +15,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
-    <PackageReference Include="XUnit" Version="2.9.3" />
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
@@ -22,6 +27,12 @@
   <ItemGroup>
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Run xunit serially: some MailboxProcessor/async tests assert from fire-and-forget
+         `Async.StartImmediate` continuations that can outlive their test collection, and
+         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Include="Misc/Aether.fs" />
     <Compile Include="Misc/Imports.fs" />
diff --git a/tests/Beam/Main.fs b/tests/Beam/Main.fs
index b00af3eaac..34ec007612 100644
--- a/tests/Beam/Main.fs
+++ b/tests/Beam/Main.fs
@@ -1,6 +1,4 @@
-#if FABLE_COMPILER
 module Program
+// No entry point: Fable does not need one here, and on .NET xunit.v3
+// generates the test runner entry point.
 ()
-#else
-module Program = let [<EntryPoint>] main _ = 0
-#endif
diff --git a/tests/Beam/xunit.runner.json b/tests/Beam/xunit.runner.json
new file mode 100644
index 0000000000..8641732346
--- /dev/null
+++ b/tests/Beam/xunit.runner.json
@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "parallelizeTestCollections": false,
+  "maxParallelThreads": 1
+}
diff --git a/tests/Php/Fable.Tests.Php.fsproj b/tests/Php/Fable.Tests.Php.fsproj
index cf4454a014..69691638f4 100644
--- a/tests/Php/Fable.Tests.Php.fsproj
+++ b/tests/Php/Fable.Tests.Php.fsproj
@@ -1,5 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
+         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
+         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+    <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
+    <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -8,7 +14,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
-    <PackageReference Include="XUnit" Version="2.9.3" />
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
@@ -17,6 +23,12 @@
   <ItemGroup>
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Run xunit serially: some async tests assert from fire-and-forget
+         `Async.StartImmediate` continuations that can outlive their test collection, and
+         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Include="Util.fs" />
     <Compile Include="TestSeq.fs" />
diff --git a/tests/Php/Main.fs b/tests/Php/Main.fs
index ae5f6f6959..34ec007612 100644
--- a/tests/Php/Main.fs
+++ b/tests/Php/Main.fs
@@ -1,6 +1,4 @@
-#if FABLE_COMPILER
 module Program
+// No entry point: Fable does not need one here, and on .NET xunit.v3
+// generates the test runner entry point.
 ()
-#else
-module Program = let [<EntryPoint>] main _ = 0
-#endif
\ No newline at end of file
diff --git a/tests/Php/xunit.runner.json b/tests/Php/xunit.runner.json
new file mode 100644
index 0000000000..8641732346
--- /dev/null
+++ b/tests/Php/xunit.runner.json
@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "parallelizeTestCollections": false,
+  "maxParallelThreads": 1
+}
diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index 0bf797f75f..338231ed34 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -1,6 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
+    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
+         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
+         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+    <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
+    <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -10,7 +15,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.6.0" />
-    <PackageReference Include="XUnit" Version="2.9.3" />
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
@@ -22,6 +27,12 @@
   <ItemGroup>
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Run xunit serially: some MailboxProcessor/async tests assert from fire-and-forget
+         `Async.StartImmediate` continuations that can outlive their test collection, and
+         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Include="../Js/Main/Globs/*.fs" />
     <Compile Include="Util.fs" />
diff --git a/tests/Python/Main.fs b/tests/Python/Main.fs
index ae5f6f6959..34ec007612 100644
--- a/tests/Python/Main.fs
+++ b/tests/Python/Main.fs
@@ -1,6 +1,4 @@
-#if FABLE_COMPILER
 module Program
+// No entry point: Fable does not need one here, and on .NET xunit.v3
+// generates the test runner entry point.
 ()
-#else
-module Program = let [<EntryPoint>] main _ = 0
-#endif
\ No newline at end of file
diff --git a/tests/Python/xunit.runner.json b/tests/Python/xunit.runner.json
new file mode 100644
index 0000000000..8641732346
--- /dev/null
+++ b/tests/Python/xunit.runner.json
@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "parallelizeTestCollections": false,
+  "maxParallelThreads": 1
+}
diff --git a/tests/Rust/Fable.Tests.Rust.fsproj b/tests/Rust/Fable.Tests.Rust.fsproj
index 5bc246aac9..c3ee88be25 100644
--- a/tests/Rust/Fable.Tests.Rust.fsproj
+++ b/tests/Rust/Fable.Tests.Rust.fsproj
@@ -1,5 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would append
+         xunit.v3's generated entry point and runner reporters after tests/src/main.fs, breaking
+         transpilation (the entry point must be the last declaration, and those sources are
+         .NET-only). Disable them for the Fable build; the real .NET build keeps them. -->
+    <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
+    <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -8,7 +15,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.6.0" />
-    <PackageReference Include="XUnit" Version="2.9.3" />
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
diff --git a/tests/Rust/tests/src/main.fs b/tests/Rust/tests/src/main.fs
index 6a938fa462..ddaf02e64b 100644
--- a/tests/Rust/tests/src/main.fs
+++ b/tests/Rust/tests/src/main.fs
@@ -7,5 +7,9 @@ let _imports() =
     ()
 
 // [<OuterAttr("cfg", [|"not(feature = \"no_std\")"|])>]
+#if FABLE_COMPILER
+// Rust needs a `fn main`, so emit the entry point when transpiling. On .NET,
+// xunit.v3 generates the test runner entry point instead (see the .fsproj).
 [<EntryPoint>]
 let main _args = 0
+#endif