Sanofi has filed a patent lawsuit against Eli Lilly, putting in place a 30-month waiting period for Eli Lilly’s Lantus biosimilar.

The lawsuit is not a surprise: Lilly indicated in last week’s earnings call that it was expected, because filing its FDA generics review application opened up a notification window, which alerted Sanofi that a potential competitor was on the block. It also put in place a stay that keeps Lilly’s drug from progressing through the regulatory pathway.

Sanofi’s suit comes with good reason—the diabetes medication earned the company almost $2 billion in third-quarter sales. In 2012, this same drug added just under $7 billion to its global coffers.