diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 9c35f3c..fa35d16 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -250,16 +250,26 @@
 #ifndef PyDict_MAXFREELIST
 #define PyDict_MAXFREELIST 80
 #endif
+
+/* bpo-40521: dict free lists are shared by all interpreters. */
+#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
+#  undef PyDict_MAXFREELIST
+#  define PyDict_MAXFREELIST 0
+#endif
+
+#if PyDict_MAXFREELIST > 0
 static PyDictObject *free_list[PyDict_MAXFREELIST];
 static int numfree = 0;
 static PyDictKeysObject *keys_free_list[PyDict_MAXFREELIST];
 static int numfreekeys = 0;
+#endif
 
 #include "clinic/dictobject.c.h"
 
 void
 _PyDict_ClearFreeList(void)
 {
+#if PyDict_MAXFREELIST > 0
     while (numfree) {
         PyDictObject *op = free_list[--numfree];
         assert(PyDict_CheckExact(op));
@@ -268,14 +278,17 @@
     while (numfreekeys) {
         PyObject_FREE(keys_free_list[--numfreekeys]);
     }
+#endif
 }
 
 /* Print summary info about the state of the optimized allocator */
 void
 _PyDict_DebugMallocStats(FILE *out)
 {
+#if PyDict_MAXFREELIST > 0
     _PyDebugAllocatorStats(out,
                            "free PyDictObject", numfree, sizeof(PyDictObject));
+#endif
 }
 
 
@@ -553,10 +566,13 @@
         es = sizeof(Py_ssize_t);
     }
 
+#if PyDict_MAXFREELIST > 0
     if (size == PyDict_MINSIZE && numfreekeys > 0) {
         dk = keys_free_list[--numfreekeys];
     }
-    else {
+    else
+#endif
+    {
         dk = PyObject_MALLOC(sizeof(PyDictKeysObject)
                              + es * size
                              + sizeof(PyDictKeyEntry) * usable);
@@ -587,10 +603,12 @@
         Py_XDECREF(entries[i].me_key);
         Py_XDECREF(entries[i].me_value);
     }
+#if PyDict_MAXFREELIST > 0
     if (keys->dk_size == PyDict_MINSIZE && numfreekeys < PyDict_MAXFREELIST) {
         keys_free_list[numfreekeys++] = keys;
         return;
     }
+#endif
     PyObject_FREE(keys);
 }
 
@@ -603,13 +621,16 @@
 {
     PyDictObject *mp;
     assert(keys != NULL);
+#if PyDict_MAXFREELIST > 0
     if (numfree) {
         mp = free_list[--numfree];
         assert (mp != NULL);
         assert (Py_IS_TYPE(mp, &PyDict_Type));
         _Py_NewReference((PyObject *)mp);
     }
-    else {
+    else
+#endif
+    {
         mp = PyObject_GC_New(PyDictObject, &PyDict_Type);
         if (mp == NULL) {
             dictkeys_decref(keys);
@@ -1258,12 +1279,15 @@
 #ifdef Py_REF_DEBUG
         _Py_RefTotal--;
 #endif
+#if PyDict_MAXFREELIST > 0
         if (oldkeys->dk_size == PyDict_MINSIZE &&
             numfreekeys < PyDict_MAXFREELIST)
         {
             keys_free_list[numfreekeys++] = oldkeys;
         }
-        else {
+        else
+#endif
+        {
             PyObject_FREE(oldkeys);
         }
     }
@@ -2005,10 +2029,15 @@
         assert(keys->dk_refcnt == 1);
         dictkeys_decref(keys);
     }
-    if (numfree < PyDict_MAXFREELIST && Py_IS_TYPE(mp, &PyDict_Type))
+#if PyDict_MAXFREELIST > 0
+    if (numfree < PyDict_MAXFREELIST && Py_IS_TYPE(mp, &PyDict_Type)) {
         free_list[numfree++] = mp;
+    }
     else
+#endif
+    {
         Py_TYPE(mp)->tp_free((PyObject *)mp);
+    }
     Py_TRASHCAN_END
 }