diff --git a/src/runtime/runtime.cs b/src/runtime/runtime.cs
index a1f9a38aa..92ff2fedd 100644
--- a/src/runtime/runtime.cs
+++ b/src/runtime/runtime.cs
@@ -751,19 +751,25 @@ public static extern int Py_Main(
         internal static extern IntPtr Py_GetBuildInfo();
 
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern int PyRun_SimpleString(string code);
+        internal static extern int PyRun_SimpleString(
+            [MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(Utf8Marshaler))] string code);
 
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern IntPtr PyRun_String(string code, IntPtr st, IntPtr globals, IntPtr locals);
+        internal static extern IntPtr PyRun_String(
+            [MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(Utf8Marshaler))] string code,
+            IntPtr st, IntPtr globals, IntPtr locals);
 
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
         internal static extern IntPtr PyEval_EvalCode(IntPtr co, IntPtr globals, IntPtr locals);
 
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern IntPtr Py_CompileString(string code, string file, IntPtr tok);
+        internal static extern IntPtr Py_CompileString(
+            [MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(Utf8Marshaler))] string code,
+            [MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(Utf8Marshaler))] string file, IntPtr tok);
 
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern IntPtr PyImport_ExecCodeModule(string name, IntPtr code);
+        internal static extern IntPtr PyImport_ExecCodeModule(
+            [MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(Utf8Marshaler))] string name, IntPtr code);
 
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
         internal static extern IntPtr PyCFunction_NewEx(IntPtr ml, IntPtr self, IntPtr mod);