diff --git a/src/runtime/Python.Runtime.csproj b/src/runtime/Python.Runtime.csproj
@@ -116,7 +116,6 @@
     <Compile Include="modulefunctionobject.cs" />
     <Compile Include="moduleobject.cs" />
     <Compile Include="modulepropertyobject.cs" />
-    <Compile Include="monosupport.cs" />
     <Compile Include="nativecall.cs" />
     <Compile Include="overload.cs" />
     <Compile Include="propertyobject.cs" />

diff --git a/src/runtime/monosupport.cs b/src/runtime/monosupport.cs
diff --git a/src/runtime/runtime.cs b/src/runtime/runtime.cs
@@ -3,10 +3,6 @@
 using System.Security;
 using System.Text;
 
-#if UCS4
-using Mono.Unix;
-#endif
-
 namespace Python.Runtime
 {
     [SuppressUnmanagedCodeSecurity()]
@@ -1656,10 +1652,32 @@ internal unsafe static extern IntPtr
             ExactSpelling = true)]
         internal unsafe static extern IntPtr
             PyUnicode_FromKindAndString(int kind,
-                [MarshalAs(UnmanagedType.CustomMarshaler,
-                    MarshalTypeRef = typeof(Utf32Marshaler))] string s,
+                IntPtr s,
                 int size);
 
+        internal static unsafe IntPtr PyUnicode_FromKindAndString(int kind,
+            string s,
+            int size)
+        {
+            var bufLength = Math.Max(s.Length, size) * 4;
+
+            IntPtr mem = Marshal.AllocHGlobal(bufLength);
+            try
+            {
+                fixed (char* ps = s)
+                {
+                    Encoding.UTF32.GetBytes(ps, s.Length, (byte*)mem, bufLength);
+                }
+
+                var result = PyUnicode_FromKindAndString(kind, mem, size);
+                return result;
+            }
+            finally
+            {
+                Marshal.FreeHGlobal(mem);
+            }
+        }
+
         internal static IntPtr PyUnicode_FromUnicode(string s, int size)
         {
             return PyUnicode_FromKindAndString(4, s, size);
@@ -1702,9 +1720,28 @@ internal unsafe static extern IntPtr
             EntryPoint = "PyUnicodeUCS4_FromUnicode",
             ExactSpelling = true)]
         internal unsafe static extern IntPtr
-            PyUnicode_FromUnicode(
-            [MarshalAs(UnmanagedType.CustomMarshaler,
-                MarshalTypeRef = typeof(Utf32Marshaler))] string s, int size);
+            PyUnicode_FromUnicode(IntPtr s, int size);
+
+        internal static unsafe IntPtr PyUnicode_FromUnicode(string s, int size)
+        {
+            var bufLength = Math.Max(s.Length, size) * 4;
+
+            IntPtr mem = Marshal.AllocHGlobal(bufLength);
+            try
+            {
+                fixed (char* ps = s)
+                {
+                    Encoding.UTF32.GetBytes(ps, s.Length, (byte*)mem, bufLength);
+                }
+
+                var result = PyUnicode_FromUnicode(mem, size);
+                return result;
+            }
+            finally
+            {
+                Marshal.FreeHGlobal(mem);
+            }
+        }
 
         [DllImport(Runtime.dll, CallingConvention = CallingConvention.Cdecl,
             EntryPoint = "PyUnicodeUCS4_GetSize",