diff --git a/src/runtime/interop.cs b/src/runtime/interop.cs
index 2e29601fd..ca3c35bfd 100644
--- a/src/runtime/interop.cs
+++ b/src/runtime/interop.cs
@@ -4,6 +4,7 @@
 using System.Runtime.InteropServices;
 using System.Reflection;
 using System.Text;
+using System.Collections.Generic;
 
 namespace Python.Runtime
 {
@@ -334,7 +335,7 @@ internal class TypeFlags
 
     internal class Interop
     {
-        private static ArrayList keepAlive;
+        private static List<ThunkInfo> keepAlive;
         private static Hashtable pmap;
 
         static Interop()
@@ -351,8 +352,7 @@ static Interop()
                 p[item.Name] = item;
             }
 
-            keepAlive = new ArrayList();
-            Marshal.AllocHGlobal(IntPtr.Size);
+            keepAlive = new List<ThunkInfo>();
             pmap = new Hashtable();
 
             pmap["tp_dealloc"] = p["DestructorFunc"];
@@ -449,7 +449,7 @@ internal static Type GetPrototype(string name)
             return pmap[name] as Type;
         }
 
-        internal static IntPtr GetThunk(MethodInfo method, string funcType = null)
+        internal static ThunkInfo GetThunk(MethodInfo method, string funcType = null)
         {
             Type dt;
             if (funcType != null)
@@ -457,18 +457,15 @@ internal static IntPtr GetThunk(MethodInfo method, string funcType = null)
             else
                 dt = GetPrototype(method.Name);
 
-            if (dt != null)
+            if (dt == null)
             {
-                IntPtr tmp = Marshal.AllocHGlobal(IntPtr.Size);
-                Delegate d = Delegate.CreateDelegate(dt, method);
-                Thunk cb = new Thunk(d);
-                Marshal.StructureToPtr(cb, tmp, false);
-                IntPtr fp = Marshal.ReadIntPtr(tmp, 0);
-                Marshal.FreeHGlobal(tmp);
-                keepAlive.Add(d);
-                return fp;
+                return ThunkInfo.Empty;
             }
-            return IntPtr.Zero;
+            Delegate d = Delegate.CreateDelegate(dt, method);
+            var info = new ThunkInfo(d);
+            // TODO: remove keepAlive when #958 merged, let the lifecycle of ThunkInfo transfer to caller.
+            keepAlive.Add(info);
+            return info;
         }
 
         [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
@@ -522,4 +519,22 @@ public Thunk(Delegate d)
             fn = d;
         }
     }
+
+    internal class ThunkInfo
+    {
+        public readonly Delegate Target;
+        public readonly IntPtr Address;
+
+        public static readonly ThunkInfo Empty = new ThunkInfo(null);
+
+        public ThunkInfo(Delegate target)
+        {
+            if (target == null)
+            {
+                return;
+            }
+            Target = target;
+            Address = Marshal.GetFunctionPointerForDelegate(target);
+        }
+    }
 }
diff --git a/src/runtime/methodwrapper.cs b/src/runtime/methodwrapper.cs
index ba92e99d4..bc7500dab 100644
--- a/src/runtime/methodwrapper.cs
+++ b/src/runtime/methodwrapper.cs
@@ -14,17 +14,19 @@ internal class MethodWrapper
         public IntPtr ptr;
         private bool _disposed = false;
 
+        private ThunkInfo _thunk;
+
         public MethodWrapper(Type type, string name, string funcType = null)
         {
             // Turn the managed method into a function pointer
 
-            IntPtr fp = Interop.GetThunk(type.GetMethod(name), funcType);
+            _thunk = Interop.GetThunk(type.GetMethod(name), funcType);
 
             // Allocate and initialize a PyMethodDef structure to represent
             // the managed method, then create a PyCFunction.
 
             mdef = Runtime.PyMem_Malloc(4 * IntPtr.Size);
-            TypeManager.WriteMethodDef(mdef, name, fp, 0x0003);
+            TypeManager.WriteMethodDef(mdef, name, _thunk.Address, 0x0003);
             ptr = Runtime.PyCFunction_NewEx(mdef, IntPtr.Zero, IntPtr.Zero);
         }
 
diff --git a/src/runtime/typemanager.cs b/src/runtime/typemanager.cs
index 97e6032cd..bb920b74f 100644
--- a/src/runtime/typemanager.cs
+++ b/src/runtime/typemanager.cs
@@ -204,8 +204,8 @@ internal static IntPtr CreateType(ManagedType impl, Type clrType)
 
         static void InitializeSlot(IntPtr type, int slotOffset, MethodInfo method)
         {
-            IntPtr thunk = Interop.GetThunk(method);
-            Marshal.WriteIntPtr(type, slotOffset, thunk);
+            var thunk = Interop.GetThunk(method);
+            Marshal.WriteIntPtr(type, slotOffset, thunk.Address);
         }
 
         internal static IntPtr CreateSubType(IntPtr py_name, IntPtr py_base_type, IntPtr py_dict)
@@ -344,16 +344,18 @@ internal static IntPtr CreateMetaType(Type impl)
             // 4 int-ptrs in size.
             IntPtr mdef = Runtime.PyMem_Malloc(3 * 4 * IntPtr.Size);
             IntPtr mdefStart = mdef;
+            ThunkInfo thunkInfo = Interop.GetThunk(typeof(MetaType).GetMethod("__instancecheck__"), "BinaryFunc");
             mdef = WriteMethodDef(
                 mdef,
                 "__instancecheck__",
-                Interop.GetThunk(typeof(MetaType).GetMethod("__instancecheck__"), "BinaryFunc")
+                thunkInfo.Address
             );
 
+            thunkInfo = Interop.GetThunk(typeof(MetaType).GetMethod("__subclasscheck__"), "BinaryFunc");
             mdef = WriteMethodDef(
                 mdef,
                 "__subclasscheck__",
-                Interop.GetThunk(typeof(MetaType).GetMethod("__subclasscheck__"), "BinaryFunc")
+                thunkInfo.Address
             );
 
             // FIXME: mdef is not used
@@ -710,7 +712,8 @@ internal static void InitializeSlots(IntPtr type, Type impl)
                         continue;
                     }
 
-                    InitializeSlot(type, Interop.GetThunk(method), name);
+                    var thunkInfo = Interop.GetThunk(method);
+                    InitializeSlot(type, thunkInfo.Address, name);
 
                     seen.Add(name);
                 }
@@ -728,8 +731,8 @@ internal static void InitializeSlots(IntPtr type, Type impl)
             // These have to be defined, though, so by default we fill these with
             // static C# functions from this class.
 
-            var ret0 = Interop.GetThunk(((Func<IntPtr, int>)Return0).Method);
-            var ret1 = Interop.GetThunk(((Func<IntPtr, int>)Return1).Method);
+            var ret0 = Interop.GetThunk(((Func<IntPtr, int>)Return0).Method).Address;
+            var ret1 = Interop.GetThunk(((Func<IntPtr, int>)Return1).Method).Address;
 
             if (native != null)
             {