diff --git a/Misc/NEWS b/Misc/NEWS
index 0bf92fd6295..594b9472cca 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -24,6 +24,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #20515: Fix NULL pointer dereference introduced by issue #20368.
+
 - Issue #19186: Restore namespacing of expat symbols inside the pyexpat module.
 
 - Issue #20053: ensurepip (and hence venv) are no longer affected by the
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index d48fb179f36..af430fba981 100644
--- a/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@ -1397,6 +1397,9 @@ varname_converter(PyObject *in, void *_out)
     if (PyUnicode_Check(in)) {
         Py_ssize_t size;
         s = PyUnicode_AsUTF8AndSize(in, &size);
+        if (s == NULL) {
+            return 0;
+        }
         if (size > INT_MAX) {
             PyErr_SetString(PyExc_OverflowError, "string is too long");
             return 0;