diff --git a/source/MongoDB.Tests/UnitTests/TestOid.cs b/source/MongoDB.Tests/UnitTests/TestOid.cs
index 6df593f7..768068a9 100644
--- a/source/MongoDB.Tests/UnitTests/TestOid.cs
+++ b/source/MongoDB.Tests/UnitTests/TestOid.cs
@@ -136,7 +136,7 @@ public void TestNotEquals()
         }
 
         [Test]
-        [ExpectedException(typeof(ArgumentNullException))]
+        [ExpectedException(typeof(ArgumentException))]
         public void TestNullValue()
         {
             new Oid(String.Empty);
diff --git a/source/MongoDB/Configuration/Mapping/Auto/AutoMappingProfile.cs b/source/MongoDB/Configuration/Mapping/Auto/AutoMappingProfile.cs
index cab3536e..135456df 100644
--- a/source/MongoDB/Configuration/Mapping/Auto/AutoMappingProfile.cs
+++ b/source/MongoDB/Configuration/Mapping/Auto/AutoMappingProfile.cs
@@ -74,7 +74,7 @@ public AutoMappingProfile()
         {
             _conventions = new ConventionProfile();
             _isSubClass = t => false;
-            _memberFinder = PublicOrProtectedMemberFinder.Instance;
+            _memberFinder = DefaultMemberFinder.Instance;
         }
 
         /// <summary>
diff --git a/source/MongoDB/Configuration/Mapping/Auto/PublicOrProtectedMemberFinder.cs b/source/MongoDB/Configuration/Mapping/Auto/DefaultMemberFinder.cs
similarity index 61%
rename from source/MongoDB/Configuration/Mapping/Auto/PublicOrProtectedMemberFinder.cs
rename to source/MongoDB/Configuration/Mapping/Auto/DefaultMemberFinder.cs
index 706bf682..bd59e419 100644
--- a/source/MongoDB/Configuration/Mapping/Auto/PublicOrProtectedMemberFinder.cs
+++ b/source/MongoDB/Configuration/Mapping/Auto/DefaultMemberFinder.cs
@@ -7,16 +7,16 @@ namespace MongoDB.Configuration.Mapping.Auto
     /// <summary>
     /// 
     /// </summary>
-    public class PublicOrProtectedMemberFinder : IMemberFinder
+    public class DefaultMemberFinder : IMemberFinder
     {
         ///<summary>
         ///</summary>
-        public static readonly PublicOrProtectedMemberFinder Instance = new PublicOrProtectedMemberFinder();
+        public static readonly DefaultMemberFinder Instance = new DefaultMemberFinder();
 
         /// <summary>
-        /// Initializes a new instance of the <see cref="PublicOrProtectedMemberFinder"/> class.
+        /// Initializes a new instance of the <see cref="DefaultMemberFinder"/> class.
         /// </summary>
-        private PublicOrProtectedMemberFinder()
+        private DefaultMemberFinder()
         {
         }
 
@@ -32,18 +32,18 @@ public IEnumerable<MemberInfo> FindMembers(Type type)
                 var getMethod = prop.GetGetMethod(true);
                 var setMethod = prop.GetSetMethod(true);
 
-                if(getMethod==null||setMethod==null)
+                if(getMethod==null || getMethod.IsPrivate || setMethod==null)
                     continue;
 
-                if(getMethod.IsPrivate||setMethod.IsPrivate)
+                if (setMethod.GetParameters().Length != 1) //an indexer
                     continue;
 
                 yield return prop;
             }
 
-            foreach (var field in type.GetFields())
+            foreach (var field in type.GetFields()) //all public fields
             {
-                if (!field.IsInitOnly && !field.IsLiteral)
+                if (!field.IsInitOnly && !field.IsLiteral) //readonly
                     yield return field;
             }
         }
diff --git a/source/MongoDB/Configuration/Mapping/Model/MemberReflectionOptimizer.cs b/source/MongoDB/Configuration/Mapping/Model/MemberReflectionOptimizer.cs
index f58bc601..c69bb35e 100644
--- a/source/MongoDB/Configuration/Mapping/Model/MemberReflectionOptimizer.cs
+++ b/source/MongoDB/Configuration/Mapping/Model/MemberReflectionOptimizer.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq.Expressions;
 using System.Reflection;
@@ -165,20 +165,18 @@ public static class MemberReflectionOptimizer
             if (!propertyInfo.CanWrite)
                 throw new InvalidOperationException("Cannot create a setter for a readonly property.");
 
-            var method = new DynamicMethod("Set" + propertyInfo.Name, null, new[] { typeof(object), typeof(object) }, true);
-            var gen = method.GetILGenerator();
+            ParameterExpression instanceParameter = Expression.Parameter(typeof(object), "target");
+            ParameterExpression valueParameter = Expression.Parameter(typeof(object), "value");
 
-            var sourceType = propertyInfo.DeclaringType;
-            var setter = propertyInfo.GetSetMethod(true);
+            Expression<Action<object, object>> lambda = Expression.Lambda<Action<object, object>>(
+                    Expression.Call(
+                        Expression.Convert(instanceParameter, propertyInfo.DeclaringType),
+                        propertyInfo.GetSetMethod(true), 
+                        Expression.Convert(valueParameter, propertyInfo.PropertyType)),
+                    instanceParameter,
+                    valueParameter);
 
-            gen.Emit(OpCodes.Ldarg_0);
-            gen.Emit(OpCodes.Castclass, sourceType);
-            gen.Emit(OpCodes.Ldarg_1);
-            gen.Emit(OpCodes.Unbox_Any, propertyInfo.PropertyType);
-            gen.Emit(OpCodes.Callvirt, setter);
-            gen.Emit(OpCodes.Ret);
-
-            var result = (Action<object, object>)method.CreateDelegate(typeof(Action<object, object>));
+            var result = lambda.Compile();
             setterCache[key] = result;
             return result;
         }
diff --git a/source/MongoDB/Linq/Translators/ProjectionBuilder.cs b/source/MongoDB/Linq/Translators/ProjectionBuilder.cs
index 13f65c34..347f94ad 100644
--- a/source/MongoDB/Linq/Translators/ProjectionBuilder.cs
+++ b/source/MongoDB/Linq/Translators/ProjectionBuilder.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Linq.Expressions;
diff --git a/source/MongoDB/MongoDB.csproj b/source/MongoDB/MongoDB.csproj
index cc0f8eab..b3ec788e 100644
--- a/source/MongoDB/MongoDB.csproj
+++ b/source/MongoDB/MongoDB.csproj
@@ -231,7 +231,7 @@
     <Compile Include="Configuration\Mapping\Auto\IAutoMappingProfile.cs" />
     <Compile Include="Configuration\Mapping\Auto\IMemberFinder.cs" />
     <Compile Include="Configuration\Mapping\Auto\MemberOverrides.cs" />
-    <Compile Include="Configuration\Mapping\Auto\PublicOrProtectedMemberFinder.cs" />
+    <Compile Include="Configuration\Mapping\Auto\DefaultMemberFinder.cs" />
     <Compile Include="Configuration\Mapping\Conventions\ConventionProfile.cs" />
     <Compile Include="Configuration\Mapping\Conventions\DefaultCollectionAdapterConvention.cs" />
     <Compile Include="Configuration\Mapping\Conventions\DefaultDefaultValueConvention.cs" />