Exhibit 31.3

CERTIFICATION

I, Ken Xie, certify that:

1. I have reviewed this Amendment No. 1 to the Annual Report on Form 10-K of Fortinet, Inc.; and

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

Date: April 30, 2018

/s/ Ken Xie

Ken Xie

Chief Executive Officer and Chairman

(Principal Executive Officer)