diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index b202e52..4f58d57 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -2590,6 +2590,7 @@
     PyObject_HEAD
     PyObject *total;
     PyObject *it;
+    PyObject *binop;
 } accumulateobject;
 
 static PyTypeObject accumulate_type;
@@ -2597,12 +2598,14 @@
 static PyObject *
 accumulate_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 {
-    static char *kwargs[] = {"iterable", NULL};
+    static char *kwargs[] = {"iterable", "func", NULL};
     PyObject *iterable;
     PyObject *it;
+    PyObject *binop = NULL;
     accumulateobject *lz;
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O:accumulate", kwargs, &iterable))
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|O:accumulate",
+                                     kwargs, &iterable, &binop))
         return NULL;
 
     /* Get iterator. */
@@ -2617,6 +2620,8 @@
         return NULL;
     }
 
+    Py_XINCREF(binop);
+    lz->binop = binop;
     lz->total = NULL;
     lz->it = it;
     return (PyObject *)lz;
@@ -2626,6 +2631,7 @@
 accumulate_dealloc(accumulateobject *lz)
 {
     PyObject_GC_UnTrack(lz);
+    Py_XDECREF(lz->binop);
     Py_XDECREF(lz->total);
     Py_XDECREF(lz->it);
     Py_TYPE(lz)->tp_free(lz);
@@ -2634,6 +2640,7 @@
 static int
 accumulate_traverse(accumulateobject *lz, visitproc visit, void *arg)
 {
+    Py_VISIT(lz->binop);
     Py_VISIT(lz->it);
     Py_VISIT(lz->total);
     return 0;
@@ -2653,8 +2660,11 @@
         lz->total = val;
         return lz->total;
     }
-   
-    newtotal = PyNumber_Add(lz->total, val);
+
+    if (lz->binop == NULL) 
+        newtotal = PyNumber_Add(lz->total, val);
+    else
+        newtotal = PyObject_CallFunctionObjArgs(lz->binop, lz->total, val, NULL);
     Py_DECREF(val);
     if (newtotal == NULL)
         return NULL;