Taylor Swift appears to have overlooked a key detail in her wedding planning — and it could spell trouble for any fans flocking to Madison Square Garden amid New York City’s crushing heat wave, sources said Thursday.

The “Cruel Summer” singer, 36, failed to submit a plan on how she’d protect Swifties who may turn up outside the Manhattan arena amid the punishing heat, according to sources familiar with the planning.

Taylor Swift failed to come up with a plan to protect her fans from the punishing heat for those Swifties flocking to Madison Square Garden for her high-profile wedding bash. Travis Kelce/Instagram

Swift and her NFL star beau Travis Kelce didn’t offer a heat mitigation plan in her permit filed with the city for the two-day event in Midtown, the sources said. Numerous streets will be closed off around the venue for the celebration.

But despite temperatures set to hit triple digits, the pop star’s team didn’t request assistance from city officials in keeping her fans cool. Her team hadn’t submitted a plan to deal with the heat as of Thursday afternoon, sources said — though air conditioning units were spotted being loaded into the arena for her guests.

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Here’s the latest on Taylor Swift and Travis Kelce’s MSG wedding:

• Jalen Brunson, NBA champion Knicks score invites to Taylor Swift-Travis Kelce MSG wedding
• Mamdani gives Taylor Swift, Travis Kelce wedding advice ahead of MSG nuptials, NYC heatwave
• More than 100 NYPD cops will be out in full force outside MSG for Taylor Swift, Travis Kelce’s NYC wedding
• Taylor Swift and Travis Kelce’s 10-hour wedding plan revealed

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Some of the measures that could be taken include handing out water, hydration packs, potentially misting and staff resources on site with the temps forecast to be unbearably hot the rest of the week.

The pop star didn’t offer a heat mitigation plan in her permit filed for the two-day event in Midtown Manhattan even as temps in the Big Apple reach triple digits and numerous streets are closed off around the venue. AP Photo/Ryan Murphy

The celeb-filled nuptials will shut down vehicular traffic in stretches of streets around the World’s Most Famous Arena starting 1 p.m., including the following:

• 7th Avenue between 30th and 34 Streets.
• West 33rd Street between 6th and 7th Avenues.
• West 32nd Street between 6th and 7th Avenues.
• West 31st Street between 6th and 7th Avenues.
• West 31st Street between 7th and 8th Avenues.

Other streets will also be shut off to pedestrians starting at 1 p.m., including:

• West side of 7th Avenue between 31st and 34th Streets
• West 33 Street between 7th and 8th Avenues.

Access to Penn Station will also be limited with riders for the subway, Amtrak, NJ Transit and LIRR advised to use entrances on the west side of 8th Avenue at 31st and 33rd Streets.

Other access points will include the northeast corner of 8th Avenue and 31st Street.

About 100 guests were expected at the Garden for a rehearsal dinner Thursday evening, with the big day set to host some 1,000 attendees on Friday.

About 130 NYPD cops are expected to be on hand outside the arena both Thursday and Friday – with the power couple picking up the tab for any overtime costs, law enforcement sources previously told The Post.

The MTA said the major event won’t disrupt public transit underground.