diff --git a/SVSim.BattleEngine.Tests/SVSim.BattleEngine.Tests.csproj b/SVSim.BattleEngine.Tests/SVSim.BattleEngine.Tests.csproj
index a4f9128..80beec2 100644
--- a/SVSim.BattleEngine.Tests/SVSim.BattleEngine.Tests.csproj
+++ b/SVSim.BattleEngine.Tests/SVSim.BattleEngine.Tests.csproj
@@ -5,7 +5,9 @@
     <!-- Match the engine: decompiled types are not nullable-clean and use explicit usings. -->
     <Nullable>disable</Nullable>
     <ImplicitUsings>disable</ImplicitUsings>
-    <LangVersion>latest</LangVersion>
+    <!-- Pinned to 12.0 (net8.0 default) to match SVSim.BattleEngine; see the rationale there
+         (the vendored decompiled engine breaks under C# 14's 'field' contextual keyword). -->
+    <LangVersion>12.0</LangVersion>
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
   </PropertyGroup>
diff --git a/SVSim.BattleEngine/SVSim.BattleEngine.csproj b/SVSim.BattleEngine/SVSim.BattleEngine.csproj
index 3a21d91..9dc3bae 100644
--- a/SVSim.BattleEngine/SVSim.BattleEngine.csproj
+++ b/SVSim.BattleEngine/SVSim.BattleEngine.csproj
@@ -5,7 +5,12 @@
     <!-- Decompiled code is not nullable-clean and uses explicit usings. -->
     <Nullable>disable</Nullable>
     <ImplicitUsings>disable</ImplicitUsings>
-    <LangVersion>latest</LangVersion>
+    <!-- Pinned to 12.0 (net8.0 default), NOT 'latest': the vendored decompiled engine uses identifiers
+         that later C# versions promoted to contextual keywords (e.g. 'field' is a string member used inside
+         a property accessor in EventDelegate.cs). Under 'latest' + a newer SDK (Rider's .NET 10 -> C# 14)
+         'field' rebinds to the synthesized backing field, breaking the build (CS1503). Pinning keeps the
+         decompiled source compiling as written regardless of the installed SDK. -->
+    <LangVersion>12.0</LangVersion>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <!-- Decompiled code triggers many benign warnings; do not fail on them. -->
     <TreatWarningsAsErrors>false</TreatWarningsAsErrors>