diff --git a/src/Compilers/CSharp/Portable/Errors/ErrorCode.cs b/src/Compilers/CSharp/Portable/Errors/ErrorCode.cs
index a5951727cc47d..1d818a47b3c07 100644
--- a/src/Compilers/CSharp/Portable/Errors/ErrorCode.cs
+++ b/src/Compilers/CSharp/Portable/Errors/ErrorCode.cs
@@ -1771,7 +1771,7 @@ internal enum ErrorCode
         ERR_NoOutputDirectory = 8771,
         ERR_StdInOptionProvidedButConsoleInputIsNotRedirected = 8772,
 
-        // available 8773
+        ERR_FeatureNotAvailableInVersion9 = 8773,
 
         WRN_MemberNotNull = 8774,
         WRN_MemberNotNullWhen = 8775,
@@ -1818,15 +1818,23 @@ internal enum ErrorCode
         ERR_AddressOfMethodGroupInExpressionTree = 8810,
         ERR_CannotConvertAddressOfToDelegate = 8811,
         ERR_AddressOfToNonFunctionPointer = 8812,
-        ERR_FeatureNotAvailableInVersion9 = 8813,
 
-        // Codes 8813, 8814, 8815, 8816 used by features/module-initializers
+        ERR_8813 = 8813, // used by features/module-initializers
+
+        ERR_8814 = 8814, // used by features/module-initializers
+
+        ERR_8815 = 8815, // used by features/module-initializers
+
+        ERR_8816 = 8816, // used by features/module-initializers
 
         ERR_PartialMethodReturnTypeDifference = 8817,
         ERR_PartialMethodRefReturnDifference = 8818,
         WRN_NullabilityMismatchInReturnTypeOnPartial = 8819,
 
-        // Codes 8820, 8821 used by features/static-lambdas
+
+        ERR_8820 = 8820, // used by features/static-lambdas
+
+        ERR_8821 = 8821, // used by features/static-lambdas
 
         ERR_ExpressionTreeContainsWithExpression = 8849,
         ERR_BadRecordDeclaration = 8850,
diff --git a/src/Compilers/CSharp/Test/Emit/Emit/EndToEndTests.cs b/src/Compilers/CSharp/Test/Emit/Emit/EndToEndTests.cs
index 0c20a4cc2e280..db9983259404f 100644
--- a/src/Compilers/CSharp/Test/Emit/Emit/EndToEndTests.cs
+++ b/src/Compilers/CSharp/Test/Emit/Emit/EndToEndTests.cs
@@ -162,7 +162,7 @@ public void DeeplyNestedGeneric()
                 (ExecutionArchitecture.x86, ExecutionConfiguration.Debug) => 460, // 270
                 (ExecutionArchitecture.x86, ExecutionConfiguration.Release) => 1310, // 1290
                 (ExecutionArchitecture.x64, ExecutionConfiguration.Debug) => 260, // 170
-                (ExecutionArchitecture.x64, ExecutionConfiguration.Release) => 750, // 730
+                (ExecutionArchitecture.x64, ExecutionConfiguration.Release) => 730, // 730
                 _ => throw new Exception($"Unexpected configuration {ExecutionConditionUtil.Architecture} {ExecutionConditionUtil.Configuration}")
             };
 
diff --git a/src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs b/src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs
index 453b8219d47d8..0286c325de004 100644
--- a/src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs
+++ b/src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs
@@ -31,6 +31,15 @@ public void Resources()
                 ErrorCode.Void,
                 ErrorCode.Unknown,
                 ErrorCode.WRN_ALinkWarn, // Not reported, but retained to allow configuring class of related warnings. See CSharpDiagnosticFilter.Filter.
+
+                // The following error codes are reserved by feature branches
+                ErrorCode.ERR_8813,
+                ErrorCode.ERR_8814,
+                ErrorCode.ERR_8815,
+                ErrorCode.ERR_8816,
+
+                ErrorCode.ERR_8820,
+                ErrorCode.ERR_8821,
             };
             foreach (ErrorCode code in Enum.GetValues(typeof(ErrorCode)))
             {