diff --git a/test/unit/TinyImageSizeTest.php b/test/unit/TinyImageSizeTest.php
index c77213ad..5db46931 100644
--- a/test/unit/TinyImageSizeTest.php
+++ b/test/unit/TinyImageSizeTest.php
@@ -194,8 +194,12 @@ public function test_resized_should_return_false_if_meta_have_output_and_not_res
 	}
 
 	public function test_will_read_mimetype_from_file() {
-		// because files in the virtual file system are not really files but empty strings, it is a text/plain.
-		$this->assertEquals( $this->original->mimetype(), 'text/plain');
+		// vfs files are empty buffers
+		// empty buffers on php < 8 returns 'text/plain', > 8 is 'application/octet-stream'
+		$this->assertContains(
+			$this->original->mimetype(),
+			array( 'text/plain', 'application/octet-stream' )
+		);
 	}
 
 	/**