After five years on top of the cybersecurity industry, Palo Alto Networks Inc. (PANW) faces a prospective decline in growth. Despite its impressive expansion of products, the industry leader simply can’t keep up with its five-year annual growth rate reaching 75%, even as cybersecurity demand continues to increase.

At the center of concerns over Palo Alto’s fall from the top, is recent guidance from the company’s last quarterly earnings report. CEO Mark McLaughlin disappointed investors with a year-over-year sales projection of 33% to 35%, representing slowing sales growth and widening losses. Palo Alto shares declined 20% in 2016, falling sharply after 2016’s fiscal fourth quarter results and rebounding back to its current trading price as of Thursday at $146.98. (For more, see: Palo Alto Networks Slashes Growth Forecast.)

Declining Growth and Heightened Competition

A significant obstacle in the way of Palo Alto’s prolonged growth is the company’s slowing sales. Sales rose 41% annually to $400.8 million last quarter, beating estimates by $11 million. Despite impressive growth, investors must note that the number represents a slowdown from 48% growth in the previous quarter, and a 59% decline from the same period last year. Total billings came in at 45%, slowing from 61% growth in the previous quarter and 69% growth YOY. As analysts project a mere 33% revenue growth in 2016, and 29% for the year after, it’s clear that although the company will continue to perform strongly, we can expect a definite cool down.

While Palo Alto ranked as the leader in the enterprise firewall market by Gartner over the past five years, the industry is quickly crowding. Startups such as Fortinet Inc. (FTNT), Check Point Software Technologies Ltd. (CHKP) and larger tech companies bundling firewalls into their product offerings pose a threat to Palo Alto’s standalone solutions. Industry giant Cisco Systems Inc. (CSCO) offers next-gen firewalls, while IBM Corp (IBM) now bundles cybersecurity offerings into its IT services, software and hardware. Increased competition could mean price reduction and a resulting hit to Palo Alto’s decelerating revenues. (To learn more, read: Fortinet: A Great Play on Cybersecurity.)

Despite Continued Growth Investors Eye Potential Red Flags

Another key indicator of the end of a company’s best growth days is the prevalence of insider selling. Palo Alto’s insiders sold 5.53 million shares over the past year, buying less than 886,000 shares, according to the Motley Fool.

Ultimately, while Palo Alto’s price-to-sales ratio rests above that of other cybersecurity rivals at over nine, investors should be aware of potential volatility that indicators such as slowed sales, increased competition and insider selling can create. While many investors remain bullish on Palo Alto stock, it will be difficult for the cybersecurity leader to maintain the magnitude of growth it has experienced over the past five years.