diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index ea46a44..1082eb4 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -198,10 +198,7 @@
 #  define OVERALLOCATE_FACTOR 4
 #endif
 
-/* bpo-40521: Interned strings are shared by all interpreters. */
-#ifndef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
-#  define INTERNED_STRINGS
-#endif
+#define INTERNED_STRINGS
 
 /* This dictionary holds all interned unicode strings.  Note that references
    to strings in this dictionary are *not* counted in the string's ob_refcnt.
@@ -288,10 +285,7 @@
 /* List of static strings. */
 static _Py_Identifier *static_strings = NULL;
 
-/* bpo-40521: Latin1 singletons are shared by all interpreters. */
-#ifndef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
-#  define LATIN1_SINGLETONS
-#endif
+#define LATIN1_SINGLETONS
 
 #ifdef LATIN1_SINGLETONS
 /* Single character Unicode strings in the Latin-1 range are being