What: Shares of Aspen Technology (AZPN) declined on Friday after the company reported its fiscal-fourth-quarter results. While Aspen beat analyst estimates for both revenue and earnings, weak guidance for fiscal 2016 sent shares lower. At 1 p.m. Friday, the stock was down about 12%.

So what: Aspen reported quarterly revenue of $114.2 million, up 12.5% year-over-year and slightly higher than analysts were expecting. Subscription and software revenue was $105.6 million, up 15.3% year-over-year, while services and other revenue was $8.5 million, down 15%.

The company reported non-GAAP EPS of $0.39, up 26% year-over-year and $0.05 higher than analysts were expecting. On a GAAP basis, EPS was $0.36, up from $0.29 during the same period last year.

Despite Aspen's beating analyst estimates, the company lowered its revenue guidance for fiscal 2016, with the new range below analyst expectations. Aspen now expects revenue between $465 million and $473 million during fiscal 2016, down from a previous range of $470 million to $478 million, and short of an average analyst estimate of $474.9 million. Guidance for EPS was raised, however, with the company expecting EPS of $1.56-$1.62 for the full year, largely above analyst expectations of $1.56.

Now what: For a stock that trades at about nine times sales, revenue growth is critical, and Aspen's revised revenue guidance was enough to send the stock tumbling despite solid results and a raised outlook for earnings. While the drop in the stock price may seem like an overreaction, revenue is now expected to grow by just 7.5% at best during fiscal 2016, compared to 12.5% growth in fiscal 2015 and 26% growth in fiscal 2014. Given this deterioration in growth, the market's reaction shouldn't be all that surprising.