diff --git a/libtests/bits.cc b/libtests/bits.cc
index c14bceb..ba1d548 100644
--- a/libtests/bits.cc
+++ b/libtests/bits.cc
@@ -3,6 +3,7 @@
 #include <qpdf/Pl_Buffer.hh>
 #include <iostream>
 #include <stdio.h>
+#include <stdlib.h>
 
 // See comments in bits.cc
 #define BITS_TESTING 1