diff --git a/src/File.php b/src/File.php
index 187645e4..604b6add 100644
--- a/src/File.php
+++ b/src/File.php
@@ -70,7 +70,7 @@ class File implements FileInterface, Stringable
         }
 
         // write data
-        $saved = @file_put_contents($filepath, $this->pointer);
+        $saved = @file_put_contents($filepath, $this->toFilePointer());
         if ($saved === false) {
             throw new NotWritableException(
                 sprintf("Can't write image data to path (%s).", $filepath)
@@ -85,7 +85,7 @@ class File implements FileInterface, Stringable
      */
     public function toString(): string
     {
-        return stream_get_contents($this->pointer, offset: 0);
+        return stream_get_contents($this->toFilePointer(), offset: 0);
     }
 
     /**
@@ -107,7 +107,7 @@ class File implements FileInterface, Stringable
      */
     public function size(): int
     {
-        $info = fstat($this->pointer);
+        $info = fstat($this->toFilePointer());
 
         return intval($info['size']);
     }
diff --git a/tests/Unit/FileTest.php b/tests/Unit/FileTest.php
index d9344e0b..0dc69897 100644
--- a/tests/Unit/FileTest.php
+++ b/tests/Unit/FileTest.php
@@ -41,11 +41,21 @@ final class FileTest extends BaseTestCase
 
     public function testSave(): void
     {
-        $filename = __DIR__ . '/file_' . strval(hrtime(true)) . '.test';
         $file = new File('foo');
-        $file->save($filename);
-        $this->assertTrue(file_exists($filename));
-        unlink($filename);
+        $filenames = [
+            __DIR__ . '/01_file_' . strval(hrtime(true)) . '.test',
+            __DIR__ . '/02_file_' . strval(hrtime(true)) . '.test',
+        ];
+
+        foreach ($filenames as $name) {
+            $file->save($name);
+        }
+
+        foreach ($filenames as $name) {
+            $this->assertFileExists($name);
+            $this->assertEquals('foo', file_get_contents($name));
+            unlink($name);
+        }
     }
 
     public function testToString(): void