diff --git a/gtsam/base/Testable.h b/gtsam/base/Testable.h
index d8829798b..a1130dfd9 100644
--- a/gtsam/base/Testable.h
+++ b/gtsam/base/Testable.h
@@ -35,6 +35,7 @@
 
 #include <boost/shared_ptr.hpp>
 #include <stdio.h>
+#include <string>
 
 #define GTSAM_PRINT(x)((x).print(#x))