diff --git a/.github/workflows/push.yml b/.github/workflows/push.yml
index 26855f0..982d61d 100644
--- a/.github/workflows/push.yml
+++ b/.github/workflows/push.yml
@@ -9,6 +9,12 @@ env:
 jobs:
   tests:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php:
+          - '7.4'
+          - '8.0'
+          - '8.1'
     steps:
       -
         name: 'Check out the repo'
@@ -19,7 +25,7 @@ jobs:
         run: 'docker login --username "$DOCKERHUB_USER" --password "$DOCKERHUB_TOKEN"'
       -
         name: 'Build image'
-        run: 'docker build -t $APP_IMAGE .'
+        run: 'docker build --build-arg="PHP_VERSION=${{ matrix.php}}" -t $APP_IMAGE .'
       -
         name: 'Run tests'
         run: 'docker run ${{env.APP_IMAGE}} composer ci'
\ No newline at end of file
diff --git a/Dockerfile b/Dockerfile
index 462ebcb..d1a199e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,5 @@
-FROM php:7.4
+ARG PHP_VERSION=8.2
+FROM php:${PHP_VERSION}
 
 ARG DEBIAN_FRONTEND=noninteractive
 ARG COMPOSER_FLAGS="--prefer-dist --no-interaction"
diff --git a/src/CsvReader.php b/src/CsvReader.php
index de343f0..40e42ee 100644
--- a/src/CsvReader.php
+++ b/src/CsvReader.php
@@ -5,6 +5,7 @@
 namespace Keboola\Csv;
 
 use Iterator;
+use ReturnTypeWillChange;
 
 class CsvReader extends AbstractCsvFile implements Iterator
 {
@@ -169,6 +170,7 @@ public function getLineBreak()
     /**
      * @inheritdoc
      */
+    #[ReturnTypeWillChange]
     public function rewind()
     {
         rewind($this->getFilePointer());
@@ -217,6 +219,7 @@ public function getLineBreakAsText()
     /**
      * @inheritdoc
      */
+    #[ReturnTypeWillChange]
     public function current()
     {
         return $this->currentRow;
@@ -225,6 +228,7 @@ public function current()
     /**
      * @inheritdoc
      */
+    #[ReturnTypeWillChange]
     public function next()
     {
         $this->currentRow = $this->readLine();
@@ -234,6 +238,7 @@ public function next()
     /**
      * @inheritdoc
      */
+    #[ReturnTypeWillChange]
     public function key()
     {
         return $this->rowCounter;
@@ -242,6 +247,7 @@ public function key()
     /**
      * @inheritdoc
      */
+    #[ReturnTypeWillChange]
     public function valid()
     {
         return $this->currentRow !== false;