diff --git a/Python/getargs.c b/Python/getargs.c
index 508055e..3fca9cd 100644
--- a/Python/getargs.c
+++ b/Python/getargs.c
@@ -206,6 +206,9 @@
 			if (level == 0)
 				max++;
 			level++;
+			if (level >= 30)
+				Py_FatalError("too many tuple nesting levels "
+					      "in argument format string");
 			break;
 		case ')':
 			if (level == 0)