diff --git a/Python/getargs.c b/Python/getargs.c
index 296a3aa2c7c..7bc150d1e47 100644
--- a/Python/getargs.c
+++ b/Python/getargs.c
@@ -261,7 +261,7 @@ vgetargs1(args, format, p_va, compat)
 	    *format != '(' &&
 	    *format != '|' && *format != ':' && *format != ';') {
 		PyErr_Format(PyExc_SystemError,
-			     "bad format string: %s", formatsave);
+			     "bad format string: %.200s", formatsave);
 		return 0;
 	}