diff --git a/com.code-philosophy.obfuz/Editor/ObfusPasses/SymbolObfus/NameMakers/NameMakerBase.cs b/com.code-philosophy.obfuz/Editor/ObfusPasses/SymbolObfus/NameMakers/NameMakerBase.cs
index 43d51c9..0173768 100644
--- a/com.code-philosophy.obfuz/Editor/ObfusPasses/SymbolObfus/NameMakers/NameMakerBase.cs
+++ b/com.code-philosophy.obfuz/Editor/ObfusPasses/SymbolObfus/NameMakers/NameMakerBase.cs
@@ -59,7 +59,7 @@ namespace Obfuz.ObfusPasses.SymbolObfus.NameMakers
 
         public bool IsNamePreserved(VirtualMethodGroup virtualMethodGroup, string name)
         {
-            return  virtualMethodGroup.methods.Any(m => GetNameScope(m.DeclaringType).IsNamePreserved(name));
+            return  virtualMethodGroup.GetNameConflictTypeScopes().Any(m => GetNameScope(m).IsNamePreserved(name));
         }
 
         private string GetDefaultNewName(object scope, string originName)
@@ -93,15 +93,15 @@ namespace Obfuz.ObfusPasses.SymbolObfus.NameMakers
             while (true)
             {
                 string newName = scope.GetNewName(originalName, false);
-                if (virtualMethodGroup.methods.Any(m => GetNameScope(m.DeclaringType).IsNamePreserved(newName)))
+                if (virtualMethodGroup.GetNameConflictTypeScopes().Any(s => GetNameScope(s).IsNamePreserved(newName)))
                 {
                     continue;
                 }
                 else
                 {
-                    foreach (var method in virtualMethodGroup.methods)
+                    foreach (var s in virtualMethodGroup.GetNameDeclaringTypeScopes())
                     {
-                        GetNameScope(method.DeclaringType).AddPreservedName(newName);
+                        GetNameScope(s).AddPreservedName(newName);
                     }
                     return newName;
                 }
diff --git a/com.code-philosophy.obfuz/Editor/ObfusPasses/SymbolObfus/VirtualMethodGroupCalculator.cs b/com.code-philosophy.obfuz/Editor/ObfusPasses/SymbolObfus/VirtualMethodGroupCalculator.cs
index c555523..1670912 100644
--- a/com.code-philosophy.obfuz/Editor/ObfusPasses/SymbolObfus/VirtualMethodGroupCalculator.cs
+++ b/com.code-philosophy.obfuz/Editor/ObfusPasses/SymbolObfus/VirtualMethodGroupCalculator.cs
@@ -12,6 +12,36 @@ namespace Obfuz.ObfusPasses.SymbolObfus
     public class VirtualMethodGroup
     {
         public List<MethodDef> methods;
+
+        private HashSet<TypeDef> _nameScopes;
+
+        public HashSet<TypeDef> GetNameConflictTypeScopes()
+        {
+            if (_nameScopes != null)
+            {
+                return _nameScopes;
+            }
+
+            _nameScopes = new HashSet<TypeDef>();
+            foreach (var method in methods)
+            {
+                TypeDef cur = method.DeclaringType;
+                while (cur != null)
+                {
+                    _nameScopes.Add(cur);
+                    cur = MetaUtil.GetBaseTypeDef(cur);
+                }
+            }
+            return _nameScopes;
+        }
+
+        public IEnumerable<TypeDef> GetNameDeclaringTypeScopes()
+        {
+            foreach (var method in methods)
+            {
+                yield return method.DeclaringType;
+            }
+        }
     }
 
     public class VirtualMethodGroupCalculator