diff -r 3275d4b584a2 Objects/dictobject.c
--- a/Objects/dictobject.c	Wed Jan 25 23:35:40 2017 -0800
+++ b/Objects/dictobject.c	Tue Feb 07 17:29:56 2017 +0900
@@ -4376,7 +4376,8 @@ int
         }
         if (value == NULL) {
             res = PyDict_DelItem(dict, key);
-            if (cached != ((PyDictObject *)dict)->ma_keys) {
+            // key sharing dict doesn't allow deletion.
+            if (cached == CACHED_KEYS(tp)) {
                 CACHED_KEYS(tp) = NULL;
                 DK_DECREF(cached);
             }
@@ -4384,7 +4385,9 @@ int
         else {
             int was_shared = cached == ((PyDictObject *)dict)->ma_keys;
             res = PyDict_SetItem(dict, key, value);
-            if (was_shared && cached != ((PyDictObject *)dict)->ma_keys) {
+            if (res == 0 && was_shared &&
+                    cached != ((PyDictObject *)dict)->ma_keys &&
+                    cached == CACHED_KEYS(tp)) {
                 /* PyDict_SetItem() may call dictresize and convert split table
                  * into combined table.  In such case, convert it to split
                  * table again and update type's shared key only when this is