diff --git a/Implab/Parsing/EnumAlphabet.cs b/Implab/Parsing/EnumAlphabet.cs
--- a/Implab/Parsing/EnumAlphabet.cs
+++ b/Implab/Parsing/EnumAlphabet.cs
@@ -16,6 +16,7 @@ namespace Implab.Parsing {
         static readonly T[] _symbols;
         static readonly EnumAlphabet<T> _fullAlphabet;
 
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1065:DoNotRaiseExceptionsInUnexpectedLocations")]
         static EnumAlphabet() {
             if (!typeof(T).IsEnum)
                 throw new InvalidOperationException("Invalid generic parameter, enumeration is required");
diff --git a/Implab/Promise.cs b/Implab/Promise.cs
--- a/Implab/Promise.cs
+++ b/Implab/Promise.cs
@@ -607,7 +607,7 @@ namespace Implab {
             }
         }
 
-        protected virtual void OnStateChanged() {
+        void OnStateChanged() {
             HandlerDescriptor handler;
             while (m_handlers.TryDequeue(out handler))
                 InvokeHandler(handler);