diff --git a/gtsam/linear/JacobianFactorUnordered.cpp b/gtsam/linear/JacobianFactorUnordered.cpp
index 43b12dd0c..7095f86b4 100644
--- a/gtsam/linear/JacobianFactorUnordered.cpp
+++ b/gtsam/linear/JacobianFactorUnordered.cpp
@@ -56,6 +56,11 @@ using namespace boost::assign;
 
 namespace gtsam {
 
+  /* ************************************************************************* */
+  JacobianFactorUnordered::JacobianFactorUnordered() :
+    Ab_(cref_list_of<1>(1), 0)
+  {}
+
   /* ************************************************************************* */
   JacobianFactorUnordered::JacobianFactorUnordered(const GaussianFactorUnordered& gf) {
     // Copy the matrix data depending on what type of factor we're copying from
@@ -82,7 +87,8 @@ namespace gtsam {
   }
 
   /* ************************************************************************* */
-  JacobianFactorUnordered::JacobianFactorUnordered(const Key i1, const Matrix& A1, Key i2, const Matrix& A2,
+  JacobianFactorUnordered::JacobianFactorUnordered(
+    const Key i1, const Matrix& A1, Key i2, const Matrix& A2,
     const Vector& b, const SharedDiagonal& model)
   {
     fillTerms(cref_list_of<2>
@@ -91,7 +97,8 @@ namespace gtsam {
   }
 
   /* ************************************************************************* */
-  JacobianFactorUnordered::JacobianFactorUnordered(const Key i1, const Matrix& A1, Key i2, const Matrix& A2,
+  JacobianFactorUnordered::JacobianFactorUnordered(
+    const Key i1, const Matrix& A1, Key i2, const Matrix& A2,
       Key i3, const Matrix& A3, const Vector& b, const SharedDiagonal& model)
   {
     fillTerms(cref_list_of<3>
diff --git a/gtsam/linear/JacobianFactorUnordered.h b/gtsam/linear/JacobianFactorUnordered.h
index 6e108fd27..04e741ebc 100644
--- a/gtsam/linear/JacobianFactorUnordered.h
+++ b/gtsam/linear/JacobianFactorUnordered.h
@@ -95,7 +95,7 @@ namespace gtsam {
     explicit JacobianFactorUnordered(const GaussianFactorUnordered& gf);
 
     /** default constructor for I/O */
-    JacobianFactorUnordered() {}
+    JacobianFactorUnordered();
 
     /** Construct Null factor */
     explicit JacobianFactorUnordered(const Vector& b_in);