diff --git a/Lib/locale.py b/Lib/locale.py
--- a/Lib/locale.py
+++ b/Lib/locale.py
@@ -442,13 +442,17 @@
         No aliasing or normalizing takes place.
 
     """
-    language, encoding = localetuple
-    if language is None:
-        language = 'C'
-    if encoding is None:
-        return language
-    else:
-        return language + '.' + encoding
+    try:
+        language, encoding = localetuple
+
+        if language is None:
+            language = 'C'
+        if encoding is None:
+            return language
+        else:
+            return language + '.' + encoding
+    except (TypeError, ValueError):
+        raise Error('Locale must be None, a string, or an iterable of two strings -- language code, encoding.')
 
 def getdefaultlocale(envvars=('LC_ALL', 'LC_CTYPE', 'LANG', 'LANGUAGE')):
 
diff --git a/Lib/test/test_locale.py b/Lib/test/test_locale.py
--- a/Lib/test/test_locale.py
+++ b/Lib/test/test_locale.py
@@ -409,6 +409,14 @@
         locale.setlocale(locale.LC_CTYPE, loc)
         self.assertEqual(loc, locale.getlocale(locale.LC_CTYPE))
 
+    def test_invalid_locale_format_in_localetuple(self):
+        with self.assertRaises(locale.Error) as e:
+            locale.setlocale(locale.LC_ALL, b'fi_FI')
+
+    def test_invalid_iterable_in_localetuple(self):
+        with self.assertRaises(locale.Error) as e:
+            locale.setlocale(locale.LC_ALL, (b'not', b'valid'))
+
 
 def test_main():
     tests = [