Twitter Inc. has an interesting reason for poor user growth in Q4 2014: a bug in Apple’s iOS 8 software update.

Apple’s new mobile operating system did not integrate properly with the Twitter software, which Twitter claims led to the loss of 4 million new users, write Sarah Frier and Tim Higgins of Bloomberg. Chief Executive Officer Dick Costolo, speaking in a conference call on Thursday, claimed that there was an “unforeseen bug in the release of iOS 8 as it related to Twitter.”

Twitter Inc Blames Apple's iOS 8 Bug For Slow Growth

iOS 8 bug affected Twitter and others

“We moved on multiple fronts to minimize its impact, but it wasn’t a one-size-fits-all fix,” Costolo said. A spokesman for Twitter added that problems arose due to an integration issue rather than a glitch in the Twitter software.

Twitter was not the only piece of software which suffered due to the introduction of iOS 8 back in September. Users reported that popular apps were more prone to crashing, and some iPhone owners said that they had to delete media files to create space for the update. Apple issued a series of software updates in an attempt to solve the problems.

The tech giant was not immediately available to comment on the impact that the update may have had on the growth of Twitter.

Encouraging signs for Twitter

Even with the bug, monthly active users rose 20% to 288 million for the December quarter. However, according to Bloomberg data, market analysts had estimated an average of 22% growth. Investors use growth in user numbers as a key measure of company growth, because Twitter is currently working towards adding advertising revenue and innovative products in its struggle to reach profitability.

As well as the effects of the iOS 8 bug, the company claimed that “seasonality” was another reason for the slowdown in the number of new users.

On a brighter note fourth-quarter revenue increased 97% to $479.1 million, while profit per share reached 12 cents per share compared with the average estimate of 6 cents. Net loss decreased to $125.4 million.

The company forecasts between 13 and 16 million new users in the first quarter of 2015, similar to 2014 levels. As of 9.34 a.m. EST the company was trading at $46.32, up 12.26% on the day.