diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -52,6 +52,7 @@
 #include <boost/filesystem/fstream.hpp>
 #include <boost/math/distributions/poisson.hpp>
 #include <boost/range/adaptor/reversed.hpp>
+#include <boost/thread.hpp>
 
 #if defined(NDEBUG)
 #error "Bitcoin cannot be compiled without assertions."