Karlovic's serve is renowned as a fearsome weapon on the men's tour
Croatia's Ivo Karlovic has had his new fastest serve world record ratified by the International Tennis Federation.
The 6ft 10in player fired down a 156mph (251kph) rocket in the fourth set of Saturday's Davis Cup doubles match against Germany in Zagreb.
The previous record was held by Andy Roddick, who hit a 155mph (249.4kph) effort in a 2004 Davis Cup tie.
"The ITF confirmed today that Ivo Karlovic broke the world record for the fastest serve," it said in a statement.
He hit his record-breaking serve in a losing cause as he and doubles partner Ivan Dodig were beaten 6-3 3-6 5-7 6-3 6-4 by Philipp Petzschner and Christopher Kas, given Germany a 2-1 overall lead.
Karlovic, 32, the tallest player in professional tennis, is currently ranked 217th in the world after time out of the game following Achilles surgery.
He has been as high as 14th in the rankings, winning four titles to date.
Karlovic also shares record for the third fastest serve - 153mph (246kph) - with Roddick and another American, Roscoe Tanner.
The Croatian hit his at the grasscourt tournament in Nottingham in 2007, Roddick's came at Queen's Club in 2004, while Tanner's 153mph effort dates back to 1978 in Palm Springs.