diff --git a/Objects/stringlib/formatter.h b/Objects/stringlib/formatter.h
index a807b97..5b7b3dc 100644
--- a/Objects/stringlib/formatter.h
+++ b/Objects/stringlib/formatter.h
@@ -649,7 +649,7 @@
     case LT_DEFAULT_LOCALE:
         locale_info->decimal_point = ".";
         locale_info->thousands_sep = ",";
-        locale_info->grouping = "\3"; /* Group every 3 characters,
+        locale_info->grouping = "\3\0"; /* Group every 3 characters,
                                          trailing 0 means repeat
                                          infinitely. */
         break;