Cloud storage company Box's revenue forecast for the current quarter missed Wall Street estimates amid slowing growth in paid customers in the fourth quarter.
The company's shares fell 12.7 percent to $21.00 in extended trading on Wednesday.
The rate of growth in paid customers slowed to 2,000 in the quarter, compared with 4,000 additions in the third quarter.
Dropbox recently filed for an initial public offering of up to $500 million.
When asked about the rival's IPO, Box Chief Executive Aaron Levie said: "I think it's really important to think about Dropbox as being in a very different market."
"... They are much more focused on consumers and small businesses whereas we are very focused on companies in the mid-market all the way up to the largest enterprises in the world," Levie told Reuters in an interview.
Analysts seemed to back up that claim.
D.A. Davidson's Rishi Jaluria said "Dropbox and Box are approaching the content collaboration market differently ... Dropbox will go public at a premium valuation to Box, which could lift Box's multiple somewhat."
The company forecast revenue for the first quarter in the range of $139 million to $140 million as per new accounting standards, below analysts' estimates of $144.3 million.
Box said it expects an adjusted loss per share for the first quarter to be in the range of 8 cents to 9 cents. Analysts on average were expecting a loss of 8 cents.
The company's net loss narrowed to $32.7 million, or 24 cents per share, in the quarter ended Jan. 31 from $36.9 million, or 28 cents per share, a year earlier.
On an adjusted basis, the loss was 6 cents per share. Analysts on average had expected a loss of 8 cents per share, according to Thomson Reuters I/B/E/S.
Redwood City, California-based Box said its revenue rose 24.3 percent to $136.7 million, in line with Wall Street estimates.