diff --git a/.travis.yml b/.travis.yml
index 6e29283c..28a9af0d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,6 +5,7 @@ php:
   - 7.2
   - 7.3
   - 7.4
+  - nightly
 
 cache:
   directories:
@@ -13,12 +14,16 @@ cache:
 
 before_script:
   # Deactivate xdebug
-  - phpenv config-rm xdebug.ini
+  - if [[ $TRAVIS_PHP_VERSION != nightly ]]; then phpenv config-rm xdebug.ini; fi
+  - if [[ $TRAVIS_PHP_VERSION == nightly ]]; then rm composer.lock; fi
   - composer install --ignore-platform-reqs
 
 script:
   - ./vendor/bin/phpunit --color=always --coverage-text
 
+allow_failures:
+  - php: nightly
+
 jobs:
   include:
 
diff --git a/composer.json b/composer.json
index 00b6fe9e..0fcb2556 100644
--- a/composer.json
+++ b/composer.json
@@ -39,7 +39,7 @@
         ]
     },
     "require": {
-        "php": "^7.2",
+        "php": "^7.2|^8.0",
         "ext-ctype": "*",
         "ext-dom": "*",
         "ext-gd": "*",
@@ -54,8 +54,8 @@
         "ext-zip": "*",
         "ext-zlib": "*",
         "maennchen/zipstream-php": "^2.1",
-        "markbaker/complex": "^1.4",
-        "markbaker/matrix": "^1.2",
+        "markbaker/complex": "^1.5|^2.0",
+        "markbaker/matrix": "^1.2|^2.0",
         "psr/simple-cache": "^1.0",
         "psr/http-client": "^1.0",
         "psr/http-factory": "^1.0"
@@ -66,14 +66,14 @@
         "jpgraph/jpgraph": "^4.0",
         "mpdf/mpdf": "^8.0",
         "phpcompatibility/php-compatibility": "^9.3",
-        "phpunit/phpunit": "^8.5",
+        "phpunit/phpunit": "^8.5|^9.3",
         "squizlabs/php_codesniffer": "^3.5",
         "tecnickcom/tcpdf": "^6.3"
     },
     "suggest": {
         "mpdf/mpdf": "Option for rendering PDF with PDF Writer",
-        "dompdf/dompdf": "Option for rendering PDF with PDF Writer",
-        "tecnickcom/tcpdf": "Option for rendering PDF with PDF Writer",
+        "dompdf/dompdf": "Option for rendering PDF with PDF Writer (doesn't yet support PHP8)",
+        "tecnickcom/tcpdf": "Option for rendering PDF with PDF Writer (doesn't yet support PHP8)",
         "jpgraph/jpgraph": "Option for rendering charts, or including charts with PDF or HTML Writers"
     },
     "autoload": {
diff --git a/samples/Basic/26_Utf8.php b/samples/Basic/26_Utf8.php
index 52a64509..52953251 100644
--- a/samples/Basic/26_Utf8.php
+++ b/samples/Basic/26_Utf8.php
@@ -12,10 +12,12 @@ $spreadsheet = $reader->load(__DIR__ . '/../templates/26template.xlsx');
 // at this point, we could do some manipulations with the template, but we skip this step
 $helper->write($spreadsheet, __FILE__, ['Xlsx', 'Xls', 'Html']);
 
-// Export to PDF (.pdf)
-$helper->log('Write to PDF format');
-IOFactory::registerWriter('Pdf', \PhpOffice\PhpSpreadsheet\Writer\Pdf\Dompdf::class);
-$helper->write($spreadsheet, __FILE__, ['Pdf']);
+if (\PHP_VERSION_ID < 80000) {
+    // Export to PDF (.pdf)
+    $helper->log('Write to PDF format');
+    IOFactory::registerWriter('Pdf', \PhpOffice\PhpSpreadsheet\Writer\Pdf\Dompdf::class);
+    $helper->write($spreadsheet, __FILE__, ['Pdf']);
+}
 
 // Remove first two rows with field headers before exporting to CSV
 $helper->log('Removing first two heading rows for CSV export');
diff --git a/samples/Pdf/21b_Pdf.php b/samples/Pdf/21b_Pdf.php
index c67ff3d2..ad2f609b 100644
--- a/samples/Pdf/21b_Pdf.php
+++ b/samples/Pdf/21b_Pdf.php
@@ -32,11 +32,13 @@ $spreadsheet->getActiveSheet()->setShowGridLines(false);
 $helper->log('Set orientation to landscape');
 $spreadsheet->getActiveSheet()->getPageSetup()->setOrientation(PageSetup::ORIENTATION_LANDSCAPE);
 
-$helper->log('Write to Dompdf');
-$writer = new Dompdf($spreadsheet);
-$filename = $helper->getFileName('21b_Pdf_dompdf.xlsx', 'pdf');
-$writer->setEditHtmlCallback('replaceBody');
-$writer->save($filename);
+if (\PHP_VERSION_ID < 80000) {
+    $helper->log('Write to Dompdf');
+    $writer = new Dompdf($spreadsheet);
+    $filename = $helper->getFileName('21b_Pdf_dompdf.xlsx', 'pdf');
+    $writer->setEditHtmlCallback('replaceBody');
+    $writer->save($filename);
+}
 
 $helper->log('Write to Mpdf');
 $writer = new Mpdf($spreadsheet);
@@ -44,8 +46,10 @@ $filename = $helper->getFileName('21b_Pdf_mpdf.xlsx', 'pdf');
 $writer->setEditHtmlCallback('replaceBody');
 $writer->save($filename);
 
-$helper->log('Write to Tcpdf');
-$writer = new Tcpdf($spreadsheet);
-$filename = $helper->getFileName('21b_Pdf_tcpdf.xlsx', 'pdf');
-$writer->setEditHtmlCallback('replaceBody');
-$writer->save($filename);
+if (\PHP_VERSION_ID < 80000) {
+    $helper->log('Write to Tcpdf');
+    $writer = new Tcpdf($spreadsheet);
+    $filename = $helper->getFileName('21b_Pdf_tcpdf.xlsx', 'pdf');
+    $writer->setEditHtmlCallback('replaceBody');
+    $writer->save($filename);
+}
diff --git a/src/PhpSpreadsheet/Reader/Csv.php b/src/PhpSpreadsheet/Reader/Csv.php
index db2b50b9..d6eb16b0 100644
--- a/src/PhpSpreadsheet/Reader/Csv.php
+++ b/src/PhpSpreadsheet/Reader/Csv.php
@@ -523,6 +523,7 @@ class Csv extends BaseReader
         // Attempt to guess mimetype
         $type = mime_content_type($pFilename);
         $supportedTypes = [
+            'application/csv',
             'text/csv',
             'text/plain',
             'inode/x-empty',
diff --git a/tests/PhpSpreadsheetTests/Functional/StreamTest.php b/tests/PhpSpreadsheetTests/Functional/StreamTest.php
index dcca6b8a..03f9a2d9 100644
--- a/tests/PhpSpreadsheetTests/Functional/StreamTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/StreamTest.php
@@ -10,16 +10,23 @@ class StreamTest extends TestCase
 {
     public function providerFormats(): array
     {
-        return [
+        $providerFormats = [
             ['Xls'],
             ['Xlsx'],
             ['Ods'],
             ['Csv'],
             ['Html'],
-            ['Tcpdf'],
-            ['Dompdf'],
             ['Mpdf'],
         ];
+
+        if (\PHP_VERSION_ID < 80000) {
+            $providerFormats = array_merge(
+                $providerFormats,
+                [['Tcpdf'], ['Dompdf']]
+            );
+        }
+
+        return $providerFormats;
     }
 
     /**
diff --git a/tests/PhpSpreadsheetTests/Helper/SampleTest.php b/tests/PhpSpreadsheetTests/Helper/SampleTest.php
index eb729dc9..369b205e 100644
--- a/tests/PhpSpreadsheetTests/Helper/SampleTest.php
+++ b/tests/PhpSpreadsheetTests/Helper/SampleTest.php
@@ -31,6 +31,16 @@ class SampleTest extends TestCase
             'Chart/32_Chart_read_write_PDF.php', // Unfortunately JpGraph is not up to date for latest PHP and raise many warnings
             'Chart/32_Chart_read_write_HTML.php', // idem
         ];
+        // TCPDF and DomPDF libraries don't support PHP8 yet
+        if (\PHP_VERSION_ID >= 80000) {
+            $skipped = array_merge(
+                $skipped,
+                [
+                    'Pdf/21_Pdf_Domdf.php',
+                    'Pdf/21_Pdf_TCPDF.php',
+                ]
+            );
+        }
 
         // Unfortunately some tests are too long be ran with code-coverage
         // analysis on Travis, so we need to exclude them
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php
index 81d4a777..83defb7b 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php
@@ -54,6 +54,7 @@ class LocaleFloatsTest extends TestCase
         preg_match('/(?:double|float)\(([^\)]+)\)/mui', ob_get_clean(), $matches);
         self::assertArrayHasKey(1, $matches);
         $actual = $matches[1];
-        self::assertEquals('1,1', $actual);
+        // From PHP8, https://wiki.php.net/rfc/locale_independent_float_to_string applies
+        self::assertEquals((\PHP_VERSION_ID < 80000) ? '1,1' : '1.1', $actual);
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataCloneTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataCloneTest.php
index d2afb423..660e40fe 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataCloneTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataCloneTest.php
@@ -5,6 +5,7 @@ namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 use PhpOffice\PhpSpreadsheet\Settings;
 use PhpOffice\PhpSpreadsheet\Shared\File;
 use PHPUnit\Framework\TestCase;
+use ZipArchive;
 
 class UnparsedDataCloneTest extends TestCase
 {
@@ -34,19 +35,20 @@ class UnparsedDataCloneTest extends TestCase
         $writer = new \PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadsheet);
         $writer->save($resultFilename);
         $dupname = 'Unable to open saved file';
-        $zip = zip_open($resultFilename);
-        if (is_resource($zip)) {
+
+        $zip = new ZipArchive();
+        if ($zip->open($resultFilename) !== false) {
             $names = [];
             $dupname = '';
-            while ($zip_entry = zip_read($zip)) {
-                $zipname = zip_entry_name($zip_entry);
-                if (in_array($zipname, $names)) {
-                    $dupname .= "$zipname,";
+            for ($index = 0; $index < $zip->numFiles; ++$index) {
+                $filename = $zip->getNameIndex($index);
+                if (in_array($filename, $names)) {
+                    $dupname .= "$filename,";
                 } else {
-                    $names[] = $zipname;
+                    $names[] = $filename;
                 }
             }
-            zip_close($zip);
+            $zip->close();
         }
         unlink($resultFilename);
         self::assertEquals('', $dupname);