diff --git a/vm/os-windows.h b/vm/os-windows.h
index 227d44af77..c5a74e5b09 100755
--- a/vm/os-windows.h
+++ b/vm/os-windows.h
@@ -20,13 +20,14 @@ typedef wchar_t F_CHAR;
 #define STRNCMP wcsncmp
 #define STRDUP _wcsdup
 
-#define CELL_FORMAT "%lu"
 
 #ifdef WIN64
+	#define CELL_FORMAT "%Iu"
         #define CELL_HEX_FORMAT "%Ix"
 	#define CELL_HEX_PAD_FORMAT "%016Ix"
         #define FIXNUM_FORMAT "%Id"
 #else
+	#define CELL_FORMAT "%lu"
         #define CELL_HEX_FORMAT "%lx"
 	#define CELL_HEX_PAD_FORMAT "%08lx"
         #define FIXNUM_FORMAT "%ld"