diff --git a/CHANGES b/CHANGES
index 8427e69..796cefc 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2,9 +2,11 @@ Temporary, post-Paramiko changelog while we get our sh!t together.
 
 ## ssh 1.7.13 (2012-MM-DD)
 
-* Moved a `fcntl` import closer to where it's used to help avoid `ImportError`
-  problems on Windows platforms. Thanks to Jason Coombs for the catch +
-  suggested fix.
+* #5: Moved a `fcntl` import closer to where it's used to help avoid
+  `ImportError` problems on Windows platforms. Thanks to Jason Coombs for the
+  catch + suggested fix.
+* #4: Updated implementation of WinPageant integration to work on 64-bit
+  Windows. Thanks again to Jason Coombs for the patch.
 
 ## ssh 1.7.12 (2012-02-10)
 
diff --git a/ssh/win_pageant.py b/ssh/win_pageant.py
index 6d0b356..e66b9fb 100644
--- a/ssh/win_pageant.py
+++ b/ssh/win_pageant.py
@@ -26,6 +26,8 @@ import struct
 import tempfile
 import mmap
 import array
+import platform
+import ctypes.wintypes
 
 # if you're on windows, you should have one of these, i guess?
 # ctypes is part of standard library since Python 2.5
@@ -73,6 +75,17 @@ def can_talk_to_agent():
         return True
     return False
 
+ULONG_PTR = ctypes.c_uint64 if platform.architecture()[0] == '64bit' else ctypes.c_uint32
+class COPYDATASTRUCT(ctypes.Structure):
+    """
+    ctypes implementation of
+    http://msdn.microsoft.com/en-us/library/windows/desktop/ms649010%28v=vs.85%29.aspx
+    """
+    _fields_ = [
+        ('num_data', ULONG_PTR),
+        ('data_size', ctypes.wintypes.DWORD),
+        ('data_loc', ctypes.c_void_p),
+        ]
 
 def _query_pageant(msg):
     hwnd = _get_pageant_window_object()
@@ -95,16 +108,14 @@ def _query_pageant(msg):
         char_buffer = array.array("c", map_filename + '\0')
         char_buffer_address, char_buffer_size = char_buffer.buffer_info()
         # Create a string to use for the SendMessage function call
-        cds = struct.pack("LLP", _AGENT_COPYDATA_ID, char_buffer_size, char_buffer_address)
+        cds = COPYDATASTRUCT(_AGENT_COPYDATA_ID, char_buffer_size, char_buffer_address)
 
         if _has_win32all:
             # win32gui.SendMessage should also allow the same pattern as
             # ctypes, but let's keep it like this for now...
-            response = win32gui.SendMessage(hwnd, win32con_WM_COPYDATA, len(cds), cds)
+            response = win32gui.SendMessage(hwnd, win32con_WM_COPYDATA, ctypes.sizeof(cds), ctypes.addressof(cds))
         elif _has_ctypes:
-            _buf = array.array('B', cds)
-            _addr, _size = _buf.buffer_info()
-            response = ctypes.windll.user32.SendMessageA(hwnd, win32con_WM_COPYDATA, _size, _addr)
+            response = ctypes.windll.user32.SendMessageA(hwnd, win32con_WM_COPYDATA, ctypes.sizeof(cds), ctypes.byref(cds))
         else:
             response = 0