diff --git a/src/adapter/etl-adapter-google-sheet/src/Flow/ETL/Adapter/GoogleSheet/Columns.php b/src/adapter/etl-adapter-google-sheet/src/Flow/ETL/Adapter/GoogleSheet/Columns.php
index 1b669bcb9..9dae9f935 100644
--- a/src/adapter/etl-adapter-google-sheet/src/Flow/ETL/Adapter/GoogleSheet/Columns.php
+++ b/src/adapter/etl-adapter-google-sheet/src/Flow/ETL/Adapter/GoogleSheet/Columns.php
@@ -17,11 +17,11 @@ public function __construct(
             throw new InvalidArgumentException('Sheet name can\'t be empty');
         }
 
-        if (!\preg_match('/^[A-Z]+$/u', $startColumn)) {
+        if (!\preg_match('/^[A-Z]+$/', $startColumn)) {
             throw new InvalidArgumentException(\sprintf('The column `%s` needs to contain only letters.', $startColumn));
         }
 
-        if (!\preg_match('/^[A-Z]+$/u', $endColumn)) {
+        if (!\preg_match('/^[A-Z]+$/', $endColumn)) {
             throw new InvalidArgumentException(\sprintf('The column `%s` needs to contain only letters.', $endColumn));
         }
 
diff --git a/src/adapter/etl-adapter-google-sheet/tests/Flow/ETL/Adapter/GoogleSheet/Tests/Unit/ColumnsTest.php b/src/adapter/etl-adapter-google-sheet/tests/Flow/ETL/Adapter/GoogleSheet/Tests/Unit/ColumnsTest.php
index ba96f7d6f..3cf38fc8b 100644
--- a/src/adapter/etl-adapter-google-sheet/tests/Flow/ETL/Adapter/GoogleSheet/Tests/Unit/ColumnsTest.php
+++ b/src/adapter/etl-adapter-google-sheet/tests/Flow/ETL/Adapter/GoogleSheet/Tests/Unit/ColumnsTest.php
@@ -5,6 +5,7 @@
 namespace Flow\ETL\Adapter\GoogleSheet\Tests\Unit;
 
 use Flow\ETL\Adapter\GoogleSheet\Columns;
+use Flow\ETL\Exception\InvalidArgumentException;
 use PHPUnit\Framework\TestCase;
 
 final class ColumnsTest extends TestCase
@@ -23,6 +24,10 @@ public static function invalid_cases() : \Generator
             'Sheet', 'AB C', 'CBA',
             'The column `AB C` needs to contain only letters.',
         ];
+        yield 'start column contains unicode' => [
+            'Sheet', 'ABĆ', 'CBA',
+            'The column `ABĆ` needs to contain only letters.',
+        ];
         yield 'end column contains number' => [
             'Sheet', 'ABC', 'CBA1',
             'The column `CBA1` needs to contain only letters.',
@@ -31,6 +36,10 @@ public static function invalid_cases() : \Generator
             'Sheet', 'ABC', 'CB A',
             'The column `CB A` needs to contain only letters.',
         ];
+        yield 'end column contains unicode' => [
+            'Sheet', 'ABC', 'ĆB',
+            'The column `ĆB` needs to contain only letters.',
+        ];
         yield 'columns in valid orders' => [
             'Sheet', 'BA', 'AB',
             'The column that starts the range `BA` must not be after the end column `AB`',
@@ -42,7 +51,9 @@ public static function invalid_cases() : \Generator
      */
     public function test_assertions(string $sheetName, string $startColumn, string $endColumn, string $expectedExceptionMessage) : void
     {
+        $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage($expectedExceptionMessage);
+
         new Columns($sheetName, $startColumn, $endColumn);
     }
 }