diff --git a/test/main.h b/test/main.h
index 9c1465e9a..a8226ab19 100644
--- a/test/main.h
+++ b/test/main.h
@@ -17,6 +17,7 @@
 #include <sstream>
 #include <vector>
 #include <typeinfo>
+#include <functional>
 
 // The following includes of STL headers have to be done _before_ the
 // definition of macros min() and max().  The reason is that many STL