diff --git a/gtsam/geometry/CameraSet.h b/gtsam/geometry/CameraSet.h
index 1db86cfde..901017bb3 100644
--- a/gtsam/geometry/CameraSet.h
+++ b/gtsam/geometry/CameraSet.h
@@ -153,7 +153,7 @@ class CameraSet : public std::vector<CAMERA, Eigen::aligned_allocator<CAMERA>> {
    * full matrices and vectors and pass it to the pointer
    * version of the function
    */
-  template <class POINT, class... OptArgs>
+  template <class POINT, class... OptArgs, typename = std::enable_if_t<sizeof...(OptArgs)!=0>>
   Vector reprojectionError(const POINT& point, const ZVector& measured,
                            OptArgs&... args) const {
     // pass it to the pointer version of the function
diff --git a/gtsam/slam/SmartFactorBase.h b/gtsam/slam/SmartFactorBase.h
index 80dde3563..e0540cc41 100644
--- a/gtsam/slam/SmartFactorBase.h
+++ b/gtsam/slam/SmartFactorBase.h
@@ -243,7 +243,7 @@ protected:
    * to the matrices and vectors that will be used to store the results instead
    * of pointers.
    */
-  template<class POINT, class ...OptArgs>
+  template<class POINT, class ...OptArgs, typename = std::enable_if_t<sizeof...(OptArgs)!=0>>
   Vector unwhitenedError(
       const Cameras& cameras, const POINT& point,
       OptArgs&&... optArgs) const {