diff --git a/xlrd/book.py b/xlrd/book.py
index 57a356a..6876a3e 100644
--- a/xlrd/book.py
+++ b/xlrd/book.py
@@ -4,6 +4,8 @@
 
 from __future__ import print_function
 
+import struct
+
 from . import compdoc, formatting, sheet
 from .biffh import *
 from .formula import *