diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 0c7def1..c9bd1cd 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -3306,6 +3306,16 @@
     vereq(2*a, "rmul")
     vereq(2.2*a, "rmul")
 
+def testipow():
+    # [SF bug 620179]
+    if verbose:
+        print "Testing correct invocation of __ipow__..."
+    class C(object):
+        def __ipow__(self, other):
+            pass
+    a = C()
+    a **= 2
+
 def do_this_first():
     if verbose:
         print "Testing SF bug 551412 ..."
@@ -3401,6 +3411,7 @@
     slottrash()
     slotmultipleinheritance()
     testrmul()
+    testipow()
     if verbose: print "All OK"
 
 if __name__ == "__main__":
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index e11b87f..ed5b829 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -3399,7 +3399,7 @@
 SLOT1(slot_nb_inplace_multiply, "__imul__", PyObject *, "O")
 SLOT1(slot_nb_inplace_divide, "__idiv__", PyObject *, "O")
 SLOT1(slot_nb_inplace_remainder, "__imod__", PyObject *, "O")
-SLOT2(slot_nb_inplace_power, "__ipow__", PyObject *, PyObject *, "OO")
+SLOT1(slot_nb_inplace_power, "__ipow__", PyObject *, "O")
 SLOT1(slot_nb_inplace_lshift, "__ilshift__", PyObject *, "O")
 SLOT1(slot_nb_inplace_rshift, "__irshift__", PyObject *, "O")
 SLOT1(slot_nb_inplace_and, "__iand__", PyObject *, "O")
@@ -4038,7 +4038,7 @@
 	IBSLOT("__imod__", nb_inplace_remainder, slot_nb_inplace_remainder,
 	       wrap_binaryfunc, "%"),
 	IBSLOT("__ipow__", nb_inplace_power, slot_nb_inplace_power,
-	       wrap_ternaryfunc, "**"),
+	       wrap_binaryfunc, "**"),
 	IBSLOT("__ilshift__", nb_inplace_lshift, slot_nb_inplace_lshift,
 	       wrap_binaryfunc, "<<"),
 	IBSLOT("__irshift__", nb_inplace_rshift, slot_nb_inplace_rshift,