diff -r f1c6e7f86bbc Lib/test/test_urlparse.py
--- a/Lib/test/test_urlparse.py	Fri Sep 27 22:14:31 2013 +0300
+++ b/Lib/test/test_urlparse.py	Sat Sep 28 16:56:36 2013 +0800
@@ -679,6 +679,20 @@
             urllib.parse.urljoin("http://python.org", b"http://python.org")
         with self.assertRaisesRegex(TypeError, "Cannot mix str"):
             urllib.parse.urljoin(b"http://python.org", "http://python.org")
+        # issue 19094
+        self.assertRaises(TypeError, urllib.parse.urljoin,
+            "http://python.org", b"")
+        self.assertRaises(TypeError, urllib.parse.urljoin,
+            b"http://python.org", "")
+        self.assertRaises(TypeError, urllib.parse.urljoin,
+            "http://python.org", [])
+        self.assertRaises(TypeError, urllib.parse.urljoin,
+            b"http://python.org", [])
+        self.assertRaises(TypeError, urllib.parse.urljoin,
+            bytearray(b"http://python.org"), [])
+        self.assertRaises(TypeError, urllib.parse.urljoin,
+            ["http://python.org"], [])
+        self.assertRaises(TypeError, urllib.parse.urljoin, [], [])
 
     def _check_result_type(self, str_type):
         num_args = len(str_type._fields)
diff -r f1c6e7f86bbc Lib/urllib/parse.py
--- a/Lib/urllib/parse.py	Fri Sep 27 22:14:31 2013 +0300
+++ b/Lib/urllib/parse.py	Sat Sep 28 16:56:36 2013 +0800
@@ -405,10 +405,15 @@
 def urljoin(base, url, allow_fragments=True):
     """Join a base URL and a possibly relative URL to form an absolute
     interpretation of the latter."""
-    if not base:
-        return url
-    if not url:
-        return base
+    base_correct_type = any((isinstance(base, str), isinstance(base, bytes),
+            isinstance(base, bytearray)))
+    url_correct_type = any((isinstance(url, str), isinstance(url, bytes),
+            isinstance(url, bytearray)))
+    if not (base_correct_type and url_correct_type):
+        raise TypeError("The first and second arguments must be str or "
+                "bytes instances")
+    if not base or not url:
+        return base + url
     base, url, _coerce_result = _coerce_args(base, url)
     bscheme, bnetloc, bpath, bparams, bquery, bfragment = \
             urlparse(base, '', allow_fragments)