Boeing Co. on Monday said certain safety alerts on its 737 MAX jets didn’t operate as airlines would have anticipated because of a previously undisclosed error on its part.

Boeing’s statement came a day after The Wall Street Journal reported the company hadn’t told airlines flying 737 MAX jets that certain safety alerts wouldn’t function as expected. The issue of nonfunctioning alerts came to light after the crash of a Lion Air jet in October in Indonesia, but there were no indications since then that it stemmed from a mistake...