diff --git a/docs/changes.txt b/docs/changes.txt
index 4cdf1bf0eb..a986c14b9c 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -589,6 +589,7 @@ wxGTK:
 wxMSW:
 
 - Fix blank wxBitmapComboBox dropdown appearance.
+- Make "%lu" work with size_t arguments under Win64 (laro).
 
 
 3.0.0: (released 2013-11-11)
diff --git a/include/wx/defs.h b/include/wx/defs.h
index 203e0f77eb..0d03f0a313 100644
--- a/include/wx/defs.h
+++ b/include/wx/defs.h
@@ -953,6 +953,10 @@ typedef wxUint16 wxWord;
             #define SIZEOF_LONG 4
         #endif
 
+        #ifndef SIZEOF_LONG_LONG
+            #define SIZEOF_LONG_LONG 8
+        #endif
+
         #ifndef SIZEOF_WCHAR_T
             /* Windows uses UTF-16 */
             #define SIZEOF_WCHAR_T 2