dll/win32/kernel32/winnls/string/format_msg.c | 30 ++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/dll/win32/kernel32/winnls/string/format_msg.c b/dll/win32/kernel32/winnls/string/format_msg.c
index ff6f083703..b5618d7300 100644
--- a/dll/win32/kernel32/winnls/string/format_msg.c
+++ b/dll/win32/kernel32/winnls/string/format_msg.c
@@ -170,6 +170,8 @@ static LPCWSTR format_insert( BOOL unicode_caller, int insert, LPCWSTR format,
     WCHAR *wstring = NULL, *p, fmt[256];
     ULONG_PTR arg;
     int size;
+    UINT64 arg64 = 0;
+    BOOL isI64 = FALSE;
 
     if (*format != '!')  /* simple string */
     {
@@ -272,15 +274,37 @@ static LPCWSTR format_insert( BOOL unicode_caller, int insert, LPCWSTR format,
     {
         *p++ = 'c';
     }
-    /* FIXME: handle I64 etc. */
-    else while (*format && *format != '!') *p++ = *format++;
+    else 
+    {
+        if (format[0] == 'I' && format[1] == '6' && format[2] == '4')
+        {
+            if (format[3] == 'u' || format[3] == 'd' ||
+                format[3] == 'i' || format[3] == 'o' ||
+                format[3] == 'x' || format[3] == 'X')
+            {
+                /* get second 32-bit value */                
+                arg64 = get_arg(insert + 1, flags, args);
+                arg64 = (arg64 << 32) | arg;
+                isI64 = TRUE;
+            }
+        }            
+        while (*format && *format != '!') *p++ = *format++;        
+    } 
 
     *p = 0;
     size = 256;
     for (;;)
     {
         WCHAR *ret = HeapAlloc( GetProcessHeap(), 0, size * sizeof(WCHAR) );
-        int needed = snprintfW( ret, size, fmt, arg );
+        int needed; 
+        if (!isI64) 
+        {
+            needed = snprintfW( ret, size, fmt, arg );
+        }
+        else
+        {
+            needed = snprintfW( ret, size, fmt, arg64 );
+        }    
         if (needed == -1 || needed >= size)
         {
             HeapFree( GetProcessHeap(), 0, ret );