A file photo shows a voter on Election Day at...

A file photo shows a voter on Election Day at the Wheatley High School in Old Westbury, Tuesday, Nov. 4, 2014. The deadline for New Yorkers intending to vote in next year's presidential primaries is a month and a half away. Credit: Steve Pfost

New Yorkers intending to vote in next year's presidential primaries should beware of a little-publicized -- but very relevant -- deadline that looms a month and a half away.

The state's major-party presidential primaries are set for April 19. Registered voters who are unaffiliated with the party whose primary they wish to vote in have only until Oct. 9 to change enrollments, according to Tom Connolly, state Board of Elections spokesman.

Previously unregistered voters have more time. They'd simply need to sign up with the party of their choice by March 25, local election officials said.

Unlike several other states, New York has a "closed primary" system. That means only registered Democrats may vote in the Democratic contest, and only Republicans get to cast ballots in the GOP primary.

The Oct. 9 enrollment-change deadline came up this month during debate discussions among Democrats.

The Democrats hold their first debate, hosted by CNN in Nevada, on Oct. 13. Some supporters of Vermont Sen. Bernie Sanders argue that's too late to offer a non-Democratic New York voter the chance to watch a debate, develop interest in a candidate and then re-enroll to vote in the Democratic primary.

By contrast, the Republicans' debate series is famously underway.

Nationally, two underdog candidates' issues go deeper. Martin O'Malley, the former Maryland governor, also criticized the debate schedule issued by the Democratic National Committee that his backers see as helping odds-on favorite Hillary Rodham Clinton deny exposure to her potential competition.

In all, six Democratic debates have been scheduled. O'Malley called for expanding that number, warning that his party would otherwise "cede the field" to the GOP, which drew 24 million viewers for its debates on Fox News earlier this month.

Sanders has said he was "disappointed but not surprised" by the short debate schedule. His supporters posted a letter to Rep. Debbie Wasserman Schultz (D-Fla.), who chairs the DNC, noting there were 26 party debates in the 2008 election cycle.

She has said the schedule offers "ample opportunity" to hear the candidates.

Virginia Sen. Jim Webb and former Rhode Island Gov. Lincoln Chafee are also due to take part. Chafee disagrees with Sanders and O'Malley. He recently said: "I think six debates is a fair number."