diff --git a/gtsam/slam/expressions.h b/gtsam/slam/expressions.h
index 6b7ffdf12..f7314c73f 100644
--- a/gtsam/slam/expressions.h
+++ b/gtsam/slam/expressions.h
@@ -20,7 +20,7 @@ typedef Expression<Point2> Point2_;
 typedef Expression<Rot2> Rot2_;
 typedef Expression<Pose2> Pose2_;
 
-Point2_ transform_to(const Pose2_& x, const Point2_& p) {
+inline Point2_ transform_to(const Pose2_& x, const Point2_& p) {
   return Point2_(x, &Pose2::transform_to, p);
 }
 
@@ -30,7 +30,7 @@ typedef Expression<Point3> Point3_;
 typedef Expression<Rot3> Rot3_;
 typedef Expression<Pose3> Pose3_;
 
-Point3_ transform_to(const Pose3_& x, const Point3_& p) {
+inline Point3_ transform_to(const Pose3_& x, const Point3_& p) {
   return Point3_(x, &Pose3::transform_to, p);
 }
 
@@ -39,7 +39,7 @@ Point3_ transform_to(const Pose3_& x, const Point3_& p) {
 typedef Expression<Cal3_S2> Cal3_S2_;
 typedef Expression<Cal3Bundler> Cal3Bundler_;
 
-Point2_ project(const Point3_& p_cam) {
+inline Point2_ project(const Point3_& p_cam) {
   return Point2_(PinholeCamera<Cal3_S2>::project_to_camera, p_cam);
 }
 
@@ -54,12 +54,12 @@ Point2_ project2(const Expression<CAMERA>& camera_, const Point3_& p_) {
   return Point2_(project4<CAMERA>, camera_, p_);
 }
 
-Point2 project6(const Pose3& x, const Point3& p, const Cal3_S2& K,
+inline Point2 project6(const Pose3& x, const Point3& p, const Cal3_S2& K,
     OptionalJacobian<2, 6> Dpose, OptionalJacobian<2, 3> Dpoint, OptionalJacobian<2, 5> Dcal) {
   return PinholeCamera<Cal3_S2>(x, K).project(p, Dpose, Dpoint, Dcal);
 }
 
-Point2_ project3(const Pose3_& x, const Point3_& p, const Cal3_S2_& K) {
+inline Point2_ project3(const Pose3_& x, const Point3_& p, const Cal3_S2_& K) {
   return Point2_(project6, x, p, K);
 }