diff --git a/src/test/diff_logic.cpp b/src/test/diff_logic.cpp
index 5147bdf3133..9a3403ad235 100644
--- a/src/test/diff_logic.cpp
+++ b/src/test/diff_logic.cpp
@@ -22,6 +22,7 @@ Revision History:
 #include "smt/smt_literal.h"
 #include "util/util.h"
 #include "util/debug.h"
+#include <iostream>
 
 struct diff_logic_ext {
     typedef rational numeral;