IBM shares fell 23% in premarket trading Tuesday after the company warned of weaker-than-expected second-quarter earnings. CEO Arvind Krishna said in a letter to investors that weakness in the infrastructure arm was worse than anticipated.

The shortfall was driven by the z17 mainframe launch stumbling and customers shifting spending toward servers, storage and memory products ahead of expected price increases. IBM now expects a 7% decline in infrastructure revenue for the year, worse than the previously guided low-single-digit decline.

For the latest quarter, IBM projects revenue of $17.2 billion and adjusted earnings of $2.93 a share, missing analyst targets of $17.9 billion and $3.01. Second-quarter EPS is expected to fall 2% year-over-year to about $2.27, with pretax margin contracting 90 basis points to 14.4%.