diff --git a/validate.h b/validate.h
index e339bb01..1d5a097e 100644
--- a/validate.h
+++ b/validate.h
@@ -9,6 +9,7 @@
 #include "misc.h"
 
 #include <iostream>
+#include <sstream>
 #include <iomanip>
 #include <ctime>
 #include <cctype>