diff --git a/phpBB/phpbb/mimetype/guesser.php b/phpBB/phpbb/mimetype/guesser.php
index c019cb5b07..8baa77089b 100644
--- a/phpBB/phpbb/mimetype/guesser.php
+++ b/phpBB/phpbb/mimetype/guesser.php
@@ -131,22 +131,22 @@ class guesser
 	 * Choose the best mime type based on the current mime type and the guess
 	 * If a guesser returns nulls or application/octet-stream, we will keep
 	 * the current guess. Guesses with a slash inside them will be favored over
-	 * already existing without slashes. However, any guess that will pass the
-	 * first check will always overwrite the default application/octet-stream.
+	 * already existing ones. However, any guess that will pass the first check
+	 * will always overwrite the default application/octet-stream.
 	 *
 	 * @param	string	$mime_type	The current mime type
 	 * @param	string	$guess		The current mime type guess
 	 *
 	 * @return string The best mime type based on current mime type and guess
 	 */
-	protected function choose_mime_type($mime_type, $guess)
+	public function choose_mime_type($mime_type, $guess)
 	{
 		if ($guess === null || $guess == 'application/octet-stream')
 		{
 			return $mime_type;
 		}
 
-		if ((strpos($mime_type, '/') === false || $mime_type == 'application/octet-stream') && strpos($guess, '/') !== false)
+		if ($mime_type == 'application/octet-stream' || strpos($guess, '/') !== false)
 		{
 			$mime_type = $guess;
 		}
diff --git a/tests/mimetype/guesser_test.php b/tests/mimetype/guesser_test.php
index b74a9f236e..fa53e6c8c4 100644
--- a/tests/mimetype/guesser_test.php
+++ b/tests/mimetype/guesser_test.php
@@ -206,4 +206,25 @@ class guesser_test extends \phpbb_test_case
 		$this->assertInstanceOf('\phpbb\mimetype\content_guesser', $guessers[0]);
 		$this->assertInstanceOf('\phpbb\mimetype\extension_guesser', $guessers[3]);
 	}
+
+	public function data_choose_mime_type()
+	{
+		return array(
+			array('application/octet-stream', 'application/octet-stream', null),
+			array('application/octet-stream', 'application/octet-stream', 'application/octet-stream'),
+			array('binary', 'application/octet-stream', 'binary'),
+			array('image/jpeg', 'application/octet-stream', 'image/jpeg'),
+			array('image/jpeg', 'binary', 'image/jpeg'),
+			array('image/jpeg', 'image/jpg', 'image/jpeg'),
+			array('image/jpeg', 'image/jpeg', 'binary'),
+		);
+	}
+
+	/**
+	 * @dataProvider data_choose_mime_type
+	 */
+	public function test_choose_mime_type($expected, $mime_type, $guess)
+	{
+		$this->assertSame($expected, $this->guesser->choose_mime_type($mime_type, $guess));
+	}
 }