diff -r 20bb8babc505 Objects/funcobject.c
--- a/Objects/funcobject.c	Wed Nov 30 12:10:54 2016 +0100
+++ b/Objects/funcobject.c	Thu Dec 01 11:04:58 2016 +0100
@@ -563,55 +563,14 @@ func_traverse(PyFunctionObject *f, visit
 }
 
 static PyObject *
-function_call(PyObject *func, PyObject *arg, PyObject *kw)
+function_call(PyObject *func, PyObject *args, PyObject *kwargs)
 {
-    PyObject *result;
-    PyObject *argdefs;
-    PyObject *kwtuple = NULL;
-    PyObject **d, **k;
-    Py_ssize_t nk, nd;
-
-    argdefs = PyFunction_GET_DEFAULTS(func);
-    if (argdefs != NULL && PyTuple_Check(argdefs)) {
-        d = &PyTuple_GET_ITEM((PyTupleObject *)argdefs, 0);
-        nd = PyTuple_GET_SIZE(argdefs);
-    }
-    else {
-        d = NULL;
-        nd = 0;
-    }
+    PyObject **stack;
+    Py_ssize_t nargs;
 
-    if (kw != NULL && PyDict_Check(kw)) {
-        Py_ssize_t pos, i;
-        nk = PyDict_Size(kw);
-        kwtuple = PyTuple_New(2*nk);
-        if (kwtuple == NULL)
-            return NULL;
-        k = &PyTuple_GET_ITEM(kwtuple, 0);
-        pos = i = 0;
-        while (PyDict_Next(kw, &pos, &k[i], &k[i+1])) {
-            Py_INCREF(k[i]);
-            Py_INCREF(k[i+1]);
-            i += 2;
-        }
-        nk = i/2;
-    }
-    else {
-        k = NULL;
-        nk = 0;
-    }
-
-    result = PyEval_EvalCodeEx(
-        PyFunction_GET_CODE(func),
-        PyFunction_GET_GLOBALS(func), (PyObject *)NULL,
-        &PyTuple_GET_ITEM(arg, 0), PyTuple_GET_SIZE(arg),
-        k, nk, d, nd,
-        PyFunction_GET_KW_DEFAULTS(func),
-        PyFunction_GET_CLOSURE(func));
-
-    Py_XDECREF(kwtuple);
-
-    return result;
+    stack = &PyTuple_GET_ITEM(args, 0);
+    nargs = PyTuple_GET_SIZE(args);
+    return _PyFunction_FastCallDict(func, stack, nargs, kwargs);
 }
 
 /* Bind a function to an object */
diff -r 20bb8babc505 Python/ceval.c
--- a/Python/ceval.c	Wed Nov 30 12:10:54 2016 +0100
+++ b/Python/ceval.c	Thu Dec 01 11:04:58 2016 +0100
@@ -4890,12 +4890,14 @@ PyObject *
 _PyFunction_FastCallDict(PyObject *func, PyObject **args, Py_ssize_t nargs,
                          PyObject *kwargs)
 {
+    /* small stack allocated on the C stack to pass 5 keyword arguments
+       (5 key+value pairs) */
+    PyObject *small_stack[2 * 5];
     PyCodeObject *co = (PyCodeObject *)PyFunction_GET_CODE(func);
     PyObject *globals = PyFunction_GET_GLOBALS(func);
     PyObject *argdefs = PyFunction_GET_DEFAULTS(func);
     PyObject *kwdefs, *closure, *name, *qualname;
-    PyObject *kwtuple, **k;
-    PyObject **d;
+    PyObject **k, **d;
     Py_ssize_t nd, nk;
     PyObject *result;
 
@@ -4925,12 +4927,20 @@ PyObject *
         Py_ssize_t pos, i;
         nk = PyDict_Size(kwargs);
 
-        kwtuple = PyTuple_New(2 * nk);
-        if (kwtuple == NULL) {
-            return NULL;
-        }
-
-        k = &PyTuple_GET_ITEM(kwtuple, 0);
+        if (nk <= (Py_ssize_t)Py_ARRAY_LENGTH(small_stack) / 2) {
+            k = small_stack;
+        }
+        else {
+            k = PyMem_Malloc((2 * nk) * sizeof(PyObject *));
+            if (k == NULL) {
+                PyErr_NoMemory();
+                return NULL;
+            }
+        }
+
+        /* We must hold strong references because kwargs can be indirectly
+           modified while the function is called: see issue #2016
+           and test_extcall */
         pos = i = 0;
         while (PyDict_Next(kwargs, &pos, &k[i], &k[i+1])) {
             Py_INCREF(k[i]);
@@ -4940,7 +4950,6 @@ PyObject *
         nk = i / 2;
     }
     else {
-        kwtuple = NULL;
         k = NULL;
         nk = 0;
     }
@@ -4964,7 +4973,19 @@ PyObject *
                                       k, k + 1, nk, 2,
                                       d, nd, kwdefs,
                                       closure, name, qualname);
-    Py_XDECREF(kwtuple);
+    if (k != NULL) {
+        Py_ssize_t i;
+
+        for (i=0; i < nk * 2; ) {
+            Py_DECREF(k[i]);
+            Py_DECREF(k[i+1]);
+            i += 2;
+        }
+
+        if (k != small_stack) {
+            PyMem_Free(k);
+        }
+    }
     return result;
 }