diff --git a/indra/test/lltut.h b/indra/test/lltut.h
index 3a0cc04281..47ea9d3f9e 100644
--- a/indra/test/lltut.h
+++ b/indra/test/lltut.h
@@ -38,6 +38,7 @@
 #include "is_approx_equal_fraction.h" // instead of llmath.h
 
 #include <tut/tut.hpp>
+#include <cstring>
 
 class LLDate;
 class LLSD;