diff -r 2b91121bc3fc Objects/dictobject.c
--- a/Objects/dictobject.c	Mon Nov 21 02:00:04 2016 -0800
+++ b/Objects/dictobject.c	Mon Nov 21 20:29:08 2016 +0900
@@ -101,6 +101,10 @@ where ix == mp->ma_used. Inserting into 
 converting the dict to the combined table.
 */
 
+#include "Python.h"
+#include "dict-common.h"
+#include "stringlib/eq.h"    /* to get unicode_eq() */
+
 /* PyDict_MINSIZE is the starting size for any new dict.
  * 8 allows dicts with no more than 5 active entries; experiments suggested
  * this suffices for the majority of dicts (consisting mostly of usually-small
@@ -110,9 +114,8 @@ converting the dict to the combined tabl
  */
 #define PyDict_MINSIZE 8
 
-#include "Python.h"
-#include "dict-common.h"
-#include "stringlib/eq.h"    /* to get unicode_eq() */
+/* PyDict_MAXSIZE is the upper bound of the dict. */
+#define PyDict_MAXSIZE (PY_SSIZE_T_MAX/8+1)
 
 /*[clinic input]
 class dict "PyDictObject *" "&PyDict_Type"
@@ -389,7 +392,7 @@ dk_set_index(PyDictKeysObject *keys, Py_
  * This can be used to reserve enough size to insert n entries without
  * resizing.
  */
-#define ESTIMATE_SIZE(n)  (((n)*3) >> 1)
+#define ESTIMATE_SIZE(n)  (((n)*3+1) >> 1)
 
 /* Alternative fraction that is otherwise close enough to 2n/3 to make
  * little difference. 8 * 2/3 == 8 * 5/8 == 5. 16 * 2/3 == 16 * 5/8 == 10.
@@ -1363,10 +1366,23 @@ PyObject *
 {
     Py_ssize_t newsize;
     PyDictKeysObject *new_keys;
-    for (newsize = PyDict_MINSIZE;
-         newsize <= minused && newsize > 0;
-         newsize <<= 1)
-        ;
+
+    if (minused < USABLE_FRACTION(PyDict_MAXSIZE)) {
+        Py_ssize_t minsize = ESTIMATE_SIZE(minused);
+        newsize = PyDict_MINSIZE;
+        while (newsize < minsize) {
+            newsize <<= 1;
+        }
+    }
+    else {
+        /* There are no strict guarantee that returned dict can contain
+         * minused items without resize.  So we create medium size dict
+         * instead of returning error when too large minused is specified.
+         */
+        newsize = 4096;
+    }
+    assert(IS_POWER_OF_2(newsize));
+
     new_keys = new_keys_object(newsize);
     if (new_keys == NULL)
         return NULL;