diff --git a/test/test_utils.py b/test/test_utils.py
index aefd94518..173c49514 100644
--- a/test/test_utils.py
+++ b/test/test_utils.py
@@ -455,6 +455,9 @@ class TestUtil(unittest.TestCase):
 
     def test_urljoin(self):
         self.assertEqual(urljoin('http://foo.de/', '/a/b/c.txt'), 'http://foo.de/a/b/c.txt')
+        self.assertEqual(urljoin(b'http://foo.de/', '/a/b/c.txt'), 'http://foo.de/a/b/c.txt')
+        self.assertEqual(urljoin('http://foo.de/', b'/a/b/c.txt'), 'http://foo.de/a/b/c.txt')
+        self.assertEqual(urljoin(b'http://foo.de/', b'/a/b/c.txt'), 'http://foo.de/a/b/c.txt')
         self.assertEqual(urljoin('//foo.de/', '/a/b/c.txt'), '//foo.de/a/b/c.txt')
         self.assertEqual(urljoin('http://foo.de/', 'a/b/c.txt'), 'http://foo.de/a/b/c.txt')
         self.assertEqual(urljoin('http://foo.de', '/a/b/c.txt'), 'http://foo.de/a/b/c.txt')
diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
index 8738aa249..d293c7498 100644
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -1748,11 +1748,16 @@ def base_url(url):
 
 
 def urljoin(base, path):
+    if isinstance(path, bytes):
+        path = path.decode('utf-8')
     if not isinstance(path, compat_str) or not path:
         return None
     if re.match(r'^(?:https?:)?//', path):
         return path
-    if not isinstance(base, compat_str) or not re.match(r'^(?:https?:)?//', base):
+    if isinstance(base, bytes):
+        base = base.decode('utf-8')
+    if not isinstance(base, compat_str) or not re.match(
+            r'^(?:https?:)?//', base):
         return None
     return compat_urlparse.urljoin(base, path)