diff --git a/gtsam/sam/RangeFactor.h b/gtsam/sam/RangeFactor.h
index 6e1a33481..a7e535646 100644
--- a/gtsam/sam/RangeFactor.h
+++ b/gtsam/sam/RangeFactor.h
@@ -126,7 +126,7 @@ class RangeFactorWithTransform
 
  private:
   /** Serialization function */
-  friend typename boost::serialization::access;
+  friend class boost::serialization::access;
   template <typename ARCHIVE>
   void serialize(ARCHIVE& ar, const unsigned int /*version*/) {
     ar& boost::serialization::make_nvp(