diff --git a/gtsam_unstable/geometry/Similarity3.cpp b/gtsam_unstable/geometry/Similarity3.cpp
index 6d38cfa69..a60ec2a24 100644
--- a/gtsam_unstable/geometry/Similarity3.cpp
+++ b/gtsam_unstable/geometry/Similarity3.cpp
@@ -189,12 +189,19 @@ Vector7 Similarity3::Logmap(const Similarity3& s, OptionalJacobian<7, 7> Hm) {
   double lambda = log(s.s_);
   Vector7 result;
   result << w, GetV(w, lambda).inverse() * s.t_.vector(), lambda;
+  if (Hm) {
+    // incomplete
+  }
   return result;
 }
 
 Similarity3 Similarity3::Expmap(const Vector7& v, OptionalJacobian<7, 7> Hm) {
   Vector3 w(v.head<3>());
   double lambda = v[6];
+  if (Hm) {
+    Matrix6 J_pose = Pose3::ExpmapDerivative(v.head<6>());
+    // incomplete
+  }
   return Similarity3(Rot3::Expmap(w), Point3(GetV(w, lambda)*v.segment<3>(3)), 1.0/exp(-lambda));
 }
 
diff --git a/gtsam_unstable/geometry/tests/testSimilarity3.cpp b/gtsam_unstable/geometry/tests/testSimilarity3.cpp
index 9ad165180..0f31a6755 100644
--- a/gtsam_unstable/geometry/tests/testSimilarity3.cpp
+++ b/gtsam_unstable/geometry/tests/testSimilarity3.cpp
@@ -49,6 +49,13 @@ static Similarity3 T3(Rot3::rodriguez(-90, 0, 0), Point3(1, 2, 3), 1);
 // Simpler transform
 Similarity3 T4(Rot3(), Point3(1, 1, 0), 2);
 
+//******************************************************************************
+TEST(Similarity3, concepts) {
+  BOOST_CONCEPT_ASSERT((IsGroup<Similarity3 >));
+  BOOST_CONCEPT_ASSERT((IsManifold<Similarity3 >));
+  BOOST_CONCEPT_ASSERT((IsLieGroup<Similarity3 >));
+}
+
 //******************************************************************************
 TEST(Similarity3, Constructors) {
   Similarity3 test;