diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index de11c090870..8a6fce9e0b4 100644
--- a/Modules/_xxsubinterpretersmodule.c
+++ b/Modules/_xxsubinterpretersmodule.c
@@ -1939,6 +1939,20 @@ _run_script_in_interpreter(PyInterpreterState *interp, const char *codestr,
         return -1;
     }
 
+#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
+    // Switch to interpreter.
+    PyThreadState *new_tstate = PyInterpreterState_ThreadHead(interp);
+    PyThreadState *save1 = PyEval_SaveThread();
+
+    (void)PyThreadState_Swap(new_tstate);
+
+    // Run the script.
+    _sharedexception *exc = NULL;
+    int result = _run_script(interp, codestr, shared, &exc);
+
+    // Switch back.
+    PyEval_RestoreThread(save1);
+#else
     // Switch to interpreter.
     PyThreadState *save_tstate = NULL;
     if (interp != PyInterpreterState_Get()) {
@@ -1956,6 +1970,7 @@ _run_script_in_interpreter(PyInterpreterState *interp, const char *codestr,
     if (save_tstate != NULL) {
         PyThreadState_Swap(save_tstate);
     }
+#endif
 
     // Propagate any exception out to the caller.
     if (exc != NULL) {