Joe Morgenstern, the Pulitzer Prize-winning film critic at the Wall Street Journal, made an awkward (see: racist) blunder in his review of the upcoming festival favourite, Lion: he confused star Dev Patel for another actor of Indian descent, Kal Penn.

"Saroo is played dazzlingly by Dev Patel, who gives his richest performance since The Namesake," Morgenstern's offending line states, referencing a role played by Penn in the 2007 Mira Nair-directed film.

US-born Penn, a Public Engagement advisor to outgoing President Barack Obama, is most famous for starring in the Harold & Kumar comedies; British-born Patel, meanwhile, prominently starred in Oscar winner Slumdog Millionaire.

Readers were quick to catch out the mistake, including one tweeter who alerted both Morgenstern and Penn to the error.

"Dev Patel wasn't in The Namesake. Did you mean the other brown actor, or other brown film?", he wrote to Morgenstern.

Morgenstern, a veteran film critic with over 50 years experience, tweeted out a hasty apology calling it a "dumb error", before issuing a more thoughtful response.

"I was angry with myself for making such a careless mistake, and after it was flagged on Twitter I tweeted impulsively, 'Dumb error'. Clearly, though, it's more than that, an error with special resonance for the times we live in," he wrote on Twitter.

"If I'd seen anything like it in someone else's column, I might well have thought the same thing many are thinking about me – just one more white guy who thinks brown or black people look alike."

"In a long career in journalism, I've done my best to nail prejudice and stupidity where I've found it, and I'll continue to do so," he continued.

"But what I wrote was offensive to many, and surely hurtful to some. I understand that, and I offer my heartfelt apology for it."

The Wall Street Journal has since posted a correction to the online review, reading: "An earlier version of this article misidentified Dev Patel as appearing in Mira Nair's The Namesake."

Lion, starring Patel, Nicole Kidman and David Wenham, is based on the true story of Hobart-based businessman Saroo Brierley, who was adopted by a Tasmanian couple while a young orphan in Kolkata.

The film, which opens locally on January 19, was a favourite at the Toronto International Film Festival last month and is expected to feature among the Best Picture and acting nominations at next year's Academy Awards.

Let's hope Kal Penn has an acceptance speech ready, just in case.