--- a/src/data.cc
+++ b/src/data.cc
@@ -5724,6 +5724,78 @@
   return retval;
 }
 
+template <class NDT>
+static NDT 
+do_accumarray_sum (const idx_vector& idx, const NDT& vals,
+                   octave_idx_type n = -1)
+{
+  typedef typename NDT::element_type T;
+  if (n < 0)
+    n = idx.extent (0);
+  else if (idx.extent (n) > n)
+    error ("accumarray: index out of range");
+
+  // FIXME: the class tree in liboctave is overly complicated, hence the
+  // following type gymnastics.
+  MArray<T> array;
+
+  if (vals.numel () == 1)
+    {
+      array = MArray<T> (n, T ());
+      array.idx_add (idx, vals (0));
+    }
+  else if (vals.length () == idx.length (n))
+    {
+      array = MArray<T> (n, T ());
+      array.idx_add (idx, MArray<T> (vals));
+    }
+  else
+    error ("accumarray: dimensions mismatch");
+
+  return NDT (MArrayN<T> (ArrayN<T> (array)));
+}
+
+DEFUN (__accumarray_sum__, args, ,
+  "-*- texinfo -*-\n\
+@deftypefn {Built-in Function} {} __accumarray_sum__ (@var{idx}, @var{vals}, @var{n})\n\
+Undocumented internal function.\n\
+@end deftypefn")
+{
+  octave_value retval;
+  int nargin = args.length ();
+  if (nargin >= 2 && nargin <= 3 && args(0).is_numeric_type ())
+    {
+      idx_vector idx = args(0).index_vector ();
+      octave_idx_type n = -1;
+      if (nargin == 3)
+        n = args(2).idx_type_value (true);
+
+      if (! error_state)
+        {
+          octave_value vals = args(1);
+          if (vals.is_single_type ())
+            {
+              if (vals.is_complex_type ())
+                retval = do_accumarray_sum (idx, vals.float_complex_array_value (), n);
+              else
+                retval = do_accumarray_sum (idx, vals.float_array_value (), n);
+            }
+          else if (vals.is_numeric_type ())
+            {
+              if (vals.is_complex_type ())
+                retval = do_accumarray_sum (idx, vals.complex_array_value (), n);
+              else
+                retval = do_accumarray_sum (idx, vals.array_value (), n);
+            }
+          else
+            gripe_wrong_type_arg ("accumarray", vals);
+        }
+    }
+  else
+    print_usage ();
+
+  return retval;  
+}
 
 
 /*