1 files changed, 4 insertions, 1 deletions
diff --git a/Modules/_json.c b/Modules/_json.c
index 5ced5c9704..e54b0b94bc 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -902,7 +902,10 @@ scan_once_unicode(PyScannerObject *s, PyObject *pystr, Py_ssize_t idx, Py_ssize_
     PyObject *res;
     Py_UNICODE *str = PyUnicode_AS_UNICODE(pystr);
     Py_ssize_t length = PyUnicode_GET_SIZE(pystr);
-    if (idx >= length) {
+    if (idx < 0)
+        /* Compatibility with Python version. */
+        idx += length;
+    if (idx < 0 || idx >= length) {
         PyErr_SetNone(PyExc_StopIteration);
         return NULL;
     }