diff --git a/gtsam/geometry/Similarity2.cpp b/gtsam/geometry/Similarity2.cpp
index 258039b5b..4b8cfd581 100644
--- a/gtsam/geometry/Similarity2.cpp
+++ b/gtsam/geometry/Similarity2.cpp
@@ -222,6 +222,10 @@ Similarity2 Similarity2::Expmap(const Vector4& v,  //
   return Similarity2(R, t, s);
 }
 
+Matrix4 Similarity2::AdjointMap() const {
+  throw std::runtime_error("Similarity2::AdjointMap not implemented");
+}
+
 std::ostream& operator<<(std::ostream& os, const Similarity2& p) {
   os << "[" << p.rotation().theta() << " " << p.translation().transpose() << " "
      << p.scale() << "]\';";
diff --git a/gtsam/geometry/Similarity2.h b/gtsam/geometry/Similarity2.h
index 0453758e0..e72cda484 100644
--- a/gtsam/geometry/Similarity2.h
+++ b/gtsam/geometry/Similarity2.h
@@ -161,6 +161,9 @@ class GTSAM_EXPORT Similarity2 : public LieGroup<Similarity2, 4> {
     }
   };
 
+  /// Project from one tangent space to another
+  Matrix4 AdjointMap() const;
+
   using LieGroup<Similarity2, 4>::inverse;
 
   /// @}