diff --git a/lib/Session.php b/lib/Session.php
index d954ade9..b3b99ba2 100644
--- a/lib/Session.php
+++ b/lib/Session.php
@@ -98,7 +98,7 @@ class Session{
 	}
 
 	public static function SetSessionCookie(string $sessionId): void{
-		setcookie('sessionid', $sessionId, ['expires' => (new DateTimeImmutable('+1 week'))->format('@'), 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => false, 'samesite' => 'Lax']); // Expires in two weeks
+		setcookie('sessionid', $sessionId, ['expires' => (new DateTimeImmutable('+1 week'))->format('U'), 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => false, 'samesite' => 'Lax']); // Expires in two weeks
 	}
 
 	/**
diff --git a/www/ebooks/download.php b/www/ebooks/download.php
index 8ba94fd8..0f42d206 100644
--- a/www/ebooks/download.php
+++ b/www/ebooks/download.php
@@ -60,7 +60,7 @@ try{
 
 	// Increment local download count, expires in 2 weeks
 	$downloadCount++;
-	setcookie('download-count', (string)$downloadCount, ['expires' => (new DateTimeImmutable('+2 week'))->format('@'), 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => false, 'samesite' => 'Lax']);
+	setcookie('download-count', (string)$downloadCount, ['expires' => (new DateTimeImmutable('+2 week'))->format('U'), 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => false, 'samesite' => 'Lax']);
 }
 catch(Exceptions\InvalidFileException | Exceptions\EbookNotFoundException){
 	Template::Emit404();
diff --git a/www/settings/post.php b/www/settings/post.php
index 842a80da..249ffe5e 100644
--- a/www/settings/post.php
+++ b/www/settings/post.php
@@ -3,7 +3,7 @@ $hideDonationAlert = HttpInput::Bool(POST, 'hide-donation-alert');
 $colorScheme = HttpInput::Str(POST, 'color-scheme');
 
 if($hideDonationAlert !== null){
-	setcookie('hide-donation-alert', $hideDonationAlert ? 'true' : 'false', ['expires' => (new DateTimeImmutable('+1 month'))->format('@'), 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => true, 'samesite' => 'Lax']);
+	setcookie('hide-donation-alert', $hideDonationAlert ? 'true' : 'false', ['expires' => (new DateTimeImmutable('+1 month'))->format('U'), 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => true, 'samesite' => 'Lax']);
 }
 
 if($colorScheme !== null){
@@ -16,7 +16,7 @@ if($colorScheme !== null){
 		setcookie('color-scheme', '', ['expires' => 0, 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => true, 'samesite' => 'Lax']);
 	}
 	else{
-		setcookie('color-scheme', $colorScheme, ['expires' => (new DateTimeImmutable('+1 year'))->format('@'), 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => true, 'samesite' => 'Lax']);
+		setcookie('color-scheme', $colorScheme, ['expires' => (new DateTimeImmutable('+1 year'))->format('U'), 'path' => '/', 'domain' => SITE_DOMAIN, 'secure' => true, 'httponly' => true, 'samesite' => 'Lax']);
 	}
 }