The strategy was to buy Apple (AAPL) shares six months before a major phone overhaul like the iPhone 6 and then sell, or even short, the shares for six months after. An investor following that advice made an average gain of 20% on part one and avoided a loss (or profited from a short) on an average decline of 5% on the back end. The strategy didn’t work in every-other years of minor iPhone upgrades like the 5S and 6S.

With about six months to go before Apple’s next expected major overhaul—the iPhone 7—some investors may be positioning for another big gain. But Deutsche Bank analyst Sherri Scribner says there are too many challenges ahead for the iPhone 7 and the once-dependable strategy won’t work this year.

“While we acknowledge many will likely buy the stock on the ‘anticipation trade’ into the iPhone 7 launch this year, we see slower smartphone sales, lack of growth at the high end, limited market share penetration in emerging markets, and elongating smartphone refresh cycles as key inhibitors to Apple’s growth longer term,” Scribner wrote in a lengthy report Wednesday. “With valuation currently reflecting long-term growth challenges, balanced by expectations for a trade into the iPhone 7 launch, we view shares as fairly valued and maintain our Hold.”

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Among the challenges, Scribner sees Apple having a hard time increasing iPhone sales in developed markets like the United States and Europe, where smartphone ownership is near a saturation point. In the U.S., 87% of households with income of $75,000 or more already have a smartphone. Most growth in the market has come among cheaper phones that cost under $300, where Apple doesn’t compete. The demise of sales subsidized by carriers is also causing customers to hold onto their old phones longer, Scribner noted.

In developing markets like China and India the trend toward cheaper phones is even more pronounced. And affordability “remains a key hurdle” for Apple in China, where 70% of phones sold for under $300 and income inequality remains stark, Scribner writes.

Scribbler also doubts that Apple’s service revenue, tallying sales from its music, storage, and app sales, can drive much growth.

“Despite the introduction of new services like Apple Music and Apple Pay, sales have only seen a modest acceleration in the past year,” she writes, noting that the company’s sales per device declined 10% last year to $17. “With this segment representing only 9% of sales, it will be difficult for Apple to grow this segment enough to drive top-line growth for the company.”

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As a final point, Scribner adds that stocks that come to represent the most valuable company by market capitalization in the S&P 500 Index, as Apple has, are typically given a lower-than-average valuation by investors. Apple currently represents just over 3% of the value of the entire index.

“We believe at a market value above 3% of the S&P 500, ownership becomes more limited, creating a situation where stocks cannot reach market multiples,” Scribner explains. “In our view, this will remain the case for Apple, which constrains the stock’s ability to reach a market multiple and suggests shares will continue to trade at a discount to the market.”