diff --git a/include/armadillo b/include/armadillo
index ed4ed3f5..5178a657 100644
--- a/include/armadillo
+++ b/include/armadillo
@@ -316,6 +316,7 @@ namespace arma
   #include "armadillo_bits/op_rcond_bones.hpp"
   #include "armadillo_bits/op_sp_plus_bones.hpp"
   #include "armadillo_bits/op_sp_minus_bones.hpp"
+  #include "armadillo_bits/op_sp_sum_bones.hpp"
   #include "armadillo_bits/op_powmat_bones.hpp"
   #include "armadillo_bits/op_rank_bones.hpp"
   #include "armadillo_bits/op_row_as_mat_bones.hpp"
@@ -354,7 +355,6 @@ namespace arma
   
   #include "armadillo_bits/spop_max_bones.hpp"
   #include "armadillo_bits/spop_min_bones.hpp"
-  #include "armadillo_bits/spop_sum_bones.hpp"
   #include "armadillo_bits/spop_strans_bones.hpp"
   #include "armadillo_bits/spop_htrans_bones.hpp"
   #include "armadillo_bits/spop_misc_bones.hpp"
@@ -764,6 +764,7 @@ namespace arma
   #include "armadillo_bits/op_rcond_meat.hpp"
   #include "armadillo_bits/op_sp_plus_meat.hpp"
   #include "armadillo_bits/op_sp_minus_meat.hpp"
+  #include "armadillo_bits/op_sp_sum_meat.hpp"
   #include "armadillo_bits/op_powmat_meat.hpp"
   #include "armadillo_bits/op_rank_meat.hpp"
   #include "armadillo_bits/op_row_as_mat_meat.hpp"
@@ -802,7 +803,6 @@ namespace arma
   
   #include "armadillo_bits/spop_max_meat.hpp"
   #include "armadillo_bits/spop_min_meat.hpp"
-  #include "armadillo_bits/spop_sum_meat.hpp"
   #include "armadillo_bits/spop_strans_meat.hpp"
   #include "armadillo_bits/spop_htrans_meat.hpp"
   #include "armadillo_bits/spop_misc_meat.hpp"
diff --git a/include/armadillo_bits/SpMat_bones.hpp b/include/armadillo_bits/SpMat_bones.hpp
index 9a91e8bf..59c64ff1 100644
--- a/include/armadillo_bits/SpMat_bones.hpp
+++ b/include/armadillo_bits/SpMat_bones.hpp
@@ -140,8 +140,7 @@ class SpMat : public SpBase< eT, SpMat<eT> >
   template<typename T1> inline SpMat& operator/=(const Op<T1, op_diagmat>& expr);
   template<typename T1> inline SpMat& operator%=(const Op<T1, op_diagmat>& expr);
   
-  //! explicit specification of sparse +/- scalar
-  template<typename T1, typename op_type> inline explicit SpMat(const SpToDOp<T1, op_type>& expr);
+  template<typename T1, typename op_type> inline SpMat(const SpToDOp<T1, op_type>& expr);
   
   //! construction of complex matrix out of two non-complex matrices
   template<typename T1, typename T2>
diff --git a/include/armadillo_bits/SpMat_meat.hpp b/include/armadillo_bits/SpMat_meat.hpp
index 247348d1..8d2dd8a4 100644
--- a/include/armadillo_bits/SpMat_meat.hpp
+++ b/include/armadillo_bits/SpMat_meat.hpp
@@ -802,12 +802,12 @@ SpMat<eT>::SpMat(const SpToDOp<T1, op_type>& expr)
   {
   arma_extra_debug_sigprint_this(this);
   
-  typedef typename T1::elem_type T;
+  typedef typename T1::elem_type T1_eT;
   
   // Make sure the type is compatible.
-  arma_type_check(( is_same_type< eT, T >::no ));
+  arma_type_check(( is_same_type< eT, T1_eT >::no ));
   
-  op_type::apply(*this, expr);
+  (*this) = Mat<eT>(expr);
   }
 
 
diff --git a/include/armadillo_bits/SpToDOp_bones.hpp b/include/armadillo_bits/SpToDOp_bones.hpp
index b8ae6ccb..bba28122 100644
--- a/include/armadillo_bits/SpToDOp_bones.hpp
+++ b/include/armadillo_bits/SpToDOp_bones.hpp
@@ -42,10 +42,13 @@ class SpToDOp : public Base< typename T1::elem_type, SpToDOp<T1, op_type> >
   
   inline explicit SpToDOp(const T1& in_m);
   inline          SpToDOp(const T1& in_m, const elem_type in_aux);
+  inline          SpToDOp(const T1& in_m, const uword     in_aux_uword_a, const uword in_aux_uword_b);
   inline         ~SpToDOp();
   
   arma_aligned const T1&       m;            //!< the operand; must be derived from SpBase
   arma_aligned       elem_type aux;          //!< auxiliary data, using the element type as used by T1
+  arma_aligned       uword     aux_uword_a;  //!< auxiliary data, uword format
+  arma_aligned       uword     aux_uword_b;  //!< auxiliary data, uword format
   
   static constexpr bool is_row  = op_type::template traits<T1>::is_row;
   static constexpr bool is_col  = op_type::template traits<T1>::is_col;
diff --git a/include/armadillo_bits/SpToDOp_meat.hpp b/include/armadillo_bits/SpToDOp_meat.hpp
index 66ab6405..4e9b501b 100644
--- a/include/armadillo_bits/SpToDOp_meat.hpp
+++ b/include/armadillo_bits/SpToDOp_meat.hpp
@@ -42,6 +42,18 @@ SpToDOp<T1, op_type>::SpToDOp(const T1& in_m, const typename T1::elem_type in_au
 
 
 
+template<typename T1, typename op_type>
+inline
+SpToDOp<T1, op_type>::SpToDOp(const T1& in_m, const uword in_aux_uword_a, const uword in_aux_uword_b)
+  : m(in_m)
+  , aux_uword_a(in_aux_uword_a)
+  , aux_uword_b(in_aux_uword_b)
+  {
+  arma_extra_debug_sigprint();
+  }
+
+
+
 template<typename T1, typename op_type>
 inline
 SpToDOp<T1, op_type>::~SpToDOp()
diff --git a/include/armadillo_bits/fn_sum.hpp b/include/armadillo_bits/fn_sum.hpp
index 0fa89369..292b90a7 100644
--- a/include/armadillo_bits/fn_sum.hpp
+++ b/include/armadillo_bits/fn_sum.hpp
@@ -115,13 +115,13 @@ typename
 enable_if2
   <
   is_arma_sparse_type<T1>::value && resolves_to_sparse_vector<T1>::no,
-  const SpOp<T1,spop_sum>
+  const SpToDOp<T1,op_sp_sum>
   >::result
 sum(const T1& x)
   {
   arma_extra_debug_sigprint();
   
-  return SpOp<T1,spop_sum>(x, 0, 0);
+  return SpToDOp<T1,op_sp_sum>(x, 0, 0);
   }
 
 
@@ -133,13 +133,13 @@ typename
 enable_if2
   <
   is_arma_sparse_type<T1>::value,
-  const SpOp<T1,spop_sum>
+  const SpToDOp<T1,op_sp_sum>
   >::result
 sum(const T1& x, const uword dim)
   {
   arma_extra_debug_sigprint();
   
-  return SpOp<T1,spop_sum>(x, dim, 0);
+  return SpToDOp<T1,op_sp_sum>(x, dim, 0);
   }
 
 
diff --git a/include/armadillo_bits/spop_sum_bones.hpp b/include/armadillo_bits/op_sp_sum_bones.hpp
similarity index 85%
rename from include/armadillo_bits/spop_sum_bones.hpp
rename to include/armadillo_bits/op_sp_sum_bones.hpp
index 2e4e5582..ee62469d 100644
--- a/include/armadillo_bits/spop_sum_bones.hpp
+++ b/include/armadillo_bits/op_sp_sum_bones.hpp
@@ -16,18 +16,11 @@
 // ------------------------------------------------------------------------
 
 
-//! \addtogroup spop_sum
-//! @{
-
-
-class spop_sum
+class op_sp_sum
   : public traits_op_xvec
   {
   public:
   
   template<typename T1>
-  inline static void apply(SpMat<typename T1::elem_type>& out, const SpOp<T1, spop_sum>& in);
+  inline static void apply(Mat<typename T1::elem_type>& out, const SpToDOp<T1, op_sp_sum>& in);
   };
-
-
-//! @}
diff --git a/include/armadillo_bits/spop_sum_meat.hpp b/include/armadillo_bits/op_sp_sum_meat.hpp
similarity index 75%
rename from include/armadillo_bits/spop_sum_meat.hpp
rename to include/armadillo_bits/op_sp_sum_meat.hpp
index 63badfd9..4f160b3e 100644
--- a/include/armadillo_bits/spop_sum_meat.hpp
+++ b/include/armadillo_bits/op_sp_sum_meat.hpp
@@ -16,21 +16,18 @@
 // ------------------------------------------------------------------------
 
 
-//! \addtogroup spop_sum
-//! @{
-
-
 
 template<typename T1>
 inline
 void
-spop_sum::apply(SpMat<typename T1::elem_type>& out, const SpOp<T1,spop_sum>& in)
+op_sp_sum::apply(Mat<typename T1::elem_type>& out, const SpToDOp<T1,op_sp_sum>& in)
   {
   arma_extra_debug_sigprint();
   
   typedef typename T1::elem_type eT;
   
   const uword dim = in.aux_uword_a;
+  
   arma_debug_check( (dim > 1), "sum(): parameter 'dim' must be 0 or 1" );
   
   const SpProxy<T1> p(in.m);
@@ -38,29 +35,24 @@ spop_sum::apply(SpMat<typename T1::elem_type>& out, const SpOp<T1,spop_sum>& in)
   const uword p_n_rows = p.get_n_rows();
   const uword p_n_cols = p.get_n_cols();
   
-  if(p.get_n_nonzero() == 0)
-    {
-    if(dim == 0)  { out.zeros(1,p_n_cols); }
-    if(dim == 1)  { out.zeros(p_n_rows,1); }
-    
-    return;
-    }
+  if(dim == 0)  { out.zeros(1, p_n_cols); }
+  if(dim == 1)  { out.zeros(p_n_rows, 1); }
   
+  if(p.get_n_nonzero() == 0)  { return; }
+  
+  eT* out_mem = out.memptr();
+    
   if(dim == 0) // find the sum in each column
     {
-    Row<eT> acc(p_n_cols, arma_zeros_indicator());
-    
-    eT* acc_mem = acc.memptr();
-    
     if(SpProxy<T1>::use_iterator)
       {
       typename SpProxy<T1>::const_iterator_type it = p.begin();
       
       const uword N = p.get_n_nonzero();
-
+      
       for(uword i=0; i < N; ++i)
         {
-        acc_mem[it.col()] += (*it);
+        out_mem[it.col()] += (*it);
         ++it;
         }
       }
@@ -68,37 +60,25 @@ spop_sum::apply(SpMat<typename T1::elem_type>& out, const SpOp<T1,spop_sum>& in)
       {
       for(uword col = 0; col < p_n_cols; ++col)
         {
-        acc_mem[col] = arrayops::accumulate
+        out_mem[col] = arrayops::accumulate
           (
           &p.get_values()[p.get_col_ptrs()[col]],
           p.get_col_ptrs()[col + 1] - p.get_col_ptrs()[col]
           );
         }
       }
-    
-    out = acc;
     }
   else
   if(dim == 1)  // find the sum in each row
     {
-    Col<eT> acc(p_n_rows, arma_zeros_indicator());
-    
-    eT* acc_mem = acc.memptr();
-    
     typename SpProxy<T1>::const_iterator_type it = p.begin();
     
     const uword N = p.get_n_nonzero();
     
     for(uword i=0; i < N; ++i)
       {
-      acc_mem[it.row()] += (*it);
+      out_mem[it.row()] += (*it);
       ++it;
       }
-    
-    out = acc;
     }
   }
-
-
-
-//! @}