Shares of Corning fell Tuesday after the optical networking company reported better-than-expected second-quarter earnings. Guidance, however, was mostly in-line with Wall Street estimates, disappointing investors.

The company posted adjusted earnings of 78 cents a share, up from 60 cents a year ago and above Wall Street expectations of 76 cents. Sales grew 17% to $4.74 billion, beating the analyst consensus call for $4.63 billion.

For the current quarter, the optical networking and glass maker forecasts adjusted earnings of 85 cents to 89 cents a share on core sales of $4.9 billion t0 $5 billion. Wall Street expects third-quarter earnings of 85 cents a share with sales totaling $4.99 billion, according to FactSet.

The stock declined 6.5% to $134 in premarket trading on Tuesday after ending Monday down 2.2%. Wall Street was taking a cautious view heading into the earnings report as Corning and other optical networking names have booked large gains over the past 12 months.