diff --git a/gtsam/inference/tests/testSymbol.cpp b/gtsam/inference/tests/testSymbol.cpp
index bedd69044..af49a1e2e 100644
--- a/gtsam/inference/tests/testSymbol.cpp
+++ b/gtsam/inference/tests/testSymbol.cpp
@@ -18,6 +18,8 @@
 
 #include <CppUnitLite/TestHarness.h>
 
+#include <sstream>
+
 using namespace std;
 using namespace gtsam;