diff --git a/Python/formatter_unicode.c b/Python/formatter_unicode.c
index 74638ca..ed95f26 100644
--- a/Python/formatter_unicode.c
+++ b/Python/formatter_unicode.c
@@ -252,8 +252,10 @@
         ++pos;
     }
     if (end-pos && READ_spec(pos) == ',') {
-        invalid_comma_and_underscore();
-        return 0;
+        if (format->thousands_separators == LT_UNDERSCORE_LOCALE) {
+            invalid_comma_and_underscore();
+            return 0;
+        }
     }
 
     /* Parse field precision */