diff -r ddc95a9bc2e0 Lib/test/test_itertools.py
--- a/Lib/test/test_itertools.py	Wed Sep 07 13:18:40 2016 +0200
+++ b/Lib/test/test_itertools.py	Thu Sep 08 17:06:48 2016 +0200
@@ -558,6 +558,7 @@
                          [Decimal('1.1'), Decimal('1.2'), Decimal('1.3')])
         self.assertEqual(take(3, count(Fraction(2,3), Fraction(1,7))),
                          [Fraction(2,3), Fraction(17,21), Fraction(20,21)])
+        self.assertEqual(take(3, count(1, 1.5)), [1, 2.5, 4.0])
         self.assertEqual(repr(take(3, count(10, 2.5))), repr([10, 12.5, 15.0]))
         c = count(3, 5)
         self.assertEqual(repr(c), 'count(3, 5)')
diff -r ddc95a9bc2e0 Modules/itertoolsmodule.c
--- a/Modules/itertoolsmodule.c	Wed Sep 07 13:18:40 2016 +0200
+++ b/Modules/itertoolsmodule.c	Thu Sep 08 17:06:48 2016 +0200
@@ -3911,7 +3911,7 @@
     Py_ssize_t cnt = 0;
     PyObject *long_cnt = NULL;
     PyObject *long_step = NULL;
-    long step;
+    double step;
     static char *kwlist[] = {"start", "step", 0};
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OO:count",
@@ -3949,8 +3949,8 @@
     assert(long_cnt != NULL && long_step != NULL);
 
     /* Fast mode only works when the step is 1 */
-    step = PyLong_AsLong(long_step);
-    if (step != 1) {
+    step = PyFloat_AsDouble(long_step);
+    if (step != 1.0) {
         slow_mode = 1;
         if (step == -1 && PyErr_Occurred())
             PyErr_Clear();