diff --git a/Src/IronPython.Modules/ResourceMetaPathImporter.cs b/Src/IronPython.Modules/ResourceMetaPathImporter.cs
index a3c444e2d..1353de8b8 100644
--- a/Src/IronPython.Modules/ResourceMetaPathImporter.cs
+++ b/Src/IronPython.Modules/ResourceMetaPathImporter.cs
@@ -69,6 +69,11 @@ fully qualified (dotted) module name. It returns the importer
 with the importer protocol."
             )]
         public object find_module(CodeContext /*!*/ context, string fullname, params object[] args) {
+            PythonContext pc = context.LanguageContext;
+
+            if (pc.BuiltinModules.TryGetValue(fullname, out Type type))
+                return null;
+
             var packedName = MakeFilename(fullname);
 
             foreach (var entry in SearchOrder) {
@@ -106,7 +111,7 @@ public object load_module(CodeContext /*!*/ context, string fullname) {
                                                   ModuleOptions.None, out script);
 
             var dict = mod.__dict__;
-            // we do these here because we don't want CompileModule to initialize the module until we've set 
+            // we do these here because we don't want CompileModule to initialize the module until we've set
             // up some additional stuff
             dict.Add("__name__", fullname);
             dict.Add("__loader__", this);
@@ -174,7 +179,7 @@ private byte[] GetCodeFromData(CodeContext /*!*/ context, bool isbytecode, Packe
 
             if (data != null) {
                 if (isbytecode) {
-                    // would put in code to unmarshal the bytecode here...                                     
+                    // would put in code to unmarshal the bytecode here...
                 }
                 else {
                     code = data;
diff --git a/Src/IronPython/Runtime/Operations/PythonOps.cs b/Src/IronPython/Runtime/Operations/PythonOps.cs
index 380c5006f..183526c52 100644
--- a/Src/IronPython/Runtime/Operations/PythonOps.cs
+++ b/Src/IronPython/Runtime/Operations/PythonOps.cs
@@ -1673,6 +1673,19 @@ public static PythonList MakeEmptyList() {
             return new PythonList();
         }
 
+        /// <summary>
+        /// Python runtime helper to create an instance of Python List object.
+        ///
+        /// List has the initial provided capacity.
+        /// </summary>
+        /// <param name="capacity">Initial list capacity</param>
+        /// <returns></returns>
+        [NoSideEffects]
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public static PythonList MakeEmptyList(int capacity) {
+            return new PythonList(capacity);
+        }
+
         /// <summary>
         /// Python runtime helper to create an instance of Tuple
         /// </summary>
diff --git a/Src/IronPython/Runtime/Operations/StringOps.cs b/Src/IronPython/Runtime/Operations/StringOps.cs
index 9a3e98a7c..fd8d02c4b 100644
--- a/Src/IronPython/Runtime/Operations/StringOps.cs
+++ b/Src/IronPython/Runtime/Operations/StringOps.cs
@@ -391,6 +391,11 @@ public static string capitalize([NotNone] this string self) {
             return Char.ToUpper(self[0], CultureInfo.InvariantCulture) + self.Substring(1).ToLower(CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Returns a copy of this string converted to lowercase
+        /// </summary>
+        public static string casefold([NotNone] this string self) => lower(self);
+
         //  default fillchar (padding char) is a space
         public static string center([NotNone] this string self, int width) {
             return center(self, width, ' ');