diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index f1dcfe9..304ea74 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -9381,6 +9381,7 @@
     PyObject *thousands_sep,
     Py_UCS4 *maxchar)
 {
+    min_width = Py_MAX(0, min_width);
     if (writer) {
         assert(digits != NULL);
         assert(maxchar == NULL);
@@ -9391,7 +9392,6 @@
     }
     assert(0 <= d_pos);
     assert(0 <= n_digits);
-    assert(0 <= min_width);
     assert(grouping != NULL);
 
     if (digits != NULL) {