diff --git a/docs/changes.txt b/docs/changes.txt
index af9241ee04..c16973f842 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -48,6 +48,13 @@ Changes in behaviour which may result in build errors
 - WXWIN_OS_DESCRIPTION doesn't exist any longer, use wxGetOsDescription().
 
 
+3.1.1: (not released yet)
+----------------------------
+
+wxMSW:
+
+- Fix crash when using wxCHMHelpController() in 64 bit builds (Xlord2).
+
 3.1.0: (released 2016-02-29)
 ----------------------------
 
diff --git a/src/msw/helpchm.cpp b/src/msw/helpchm.cpp
index a819a28458..f948f56d51 100644
--- a/src/msw/helpchm.cpp
+++ b/src/msw/helpchm.cpp
@@ -36,10 +36,10 @@
 // ----------------------------------------------------------------------------
 
 #ifndef UNICODE
-    typedef HWND ( WINAPI * HTMLHELP )( HWND, LPCSTR, UINT, DWORD );
+    typedef HWND ( WINAPI * HTMLHELP )( HWND, LPCSTR, UINT, ULONG_PTR );
     #define HTMLHELP_NAME wxT("HtmlHelpA")
 #else // ANSI
-    typedef HWND ( WINAPI * HTMLHELP )( HWND, LPCWSTR, UINT, DWORD );
+    typedef HWND ( WINAPI * HTMLHELP )( HWND, LPCWSTR, UINT, ULONG_PTR );
     #define HTMLHELP_NAME wxT("HtmlHelpW")
 #endif