diff --git a/gtsam/inference/Factor.h b/gtsam/inference/Factor.h
index e357a9c88..074151e16 100644
--- a/gtsam/inference/Factor.h
+++ b/gtsam/inference/Factor.h
@@ -24,12 +24,13 @@
 #ifdef GTSAM_ENABLE_BOOST_SERIALIZATION
 #include <boost/serialization/nvp.hpp>
 #endif
-#include <memory>
-
-#include <gtsam/base/types.h>
 #include <gtsam/base/FastVector.h>
+#include <gtsam/base/types.h>
 #include <gtsam/inference/Key.h>
 
+#include <algorithm>
+#include <memory>
+
 namespace gtsam {
 
   /// Define collection types: