diff --git a/lib/sql.py b/lib/sql.py
index a5043dcc..8be6542e 100644
--- a/lib/sql.py
+++ b/lib/sql.py
@@ -204,7 +204,7 @@ re_compose = re.compile("""
     """, re.VERBOSE)
 
 
-def compose(sql, args=None):
+def compose(sql, args=()):
     phs = list(re_compose.finditer(sql))
 
     # check placeholders consistent
@@ -240,8 +240,8 @@ def compose(sql, args=None):
         return _compose_map(sql, phs, args)
 
     else:
-        if not isinstance(args, collections.Sequence) and args:
-            raise TypeError(
+        if isinstance(args, collections.Sequence) and args:
+            raise ValueError(
                 "the sql string expects no value, got %s instead" % len(args))
         # If args are a mapping, no placeholder is an acceptable case
 
@@ -267,7 +267,7 @@ def _compose_seq(sql, phs, args):
     if phs:
         rv.append(SQL(sql[phs[-1].end():]))
     else:
-        rv.append(sql)
+        rv.append(SQL(sql))
 
     return Composed(rv)
 
diff --git a/tests/test_sql.py b/tests/test_sql.py
index c8ec716b..f7c0801b 100755
--- a/tests/test_sql.py
+++ b/tests/test_sql.py
@@ -55,6 +55,21 @@ class ComposeTests(ConnectingTestCase):
         s1 = s.as_string(self.conn)
         self.assertEqual(s1, "select '2016-12-31'::date;")
 
+    def test_compose_empty(self):
+        s = sql.compose("select foo;")
+        s1 = s.as_string(self.conn)
+        self.assertEqual(s1, "select foo;")
+
+    def test_compose_badnargs(self):
+        self.assertRaises(ValueError, sql.compose, "select foo;", [10])
+        self.assertRaises(ValueError, sql.compose, "select %s;")
+        self.assertRaises(ValueError, sql.compose, "select %s;", [])
+        self.assertRaises(ValueError, sql.compose, "select %s;", [10, 20])
+
+    def test_compose_bad_args_type(self):
+        self.assertRaises(TypeError, sql.compose, "select %s;", {'a': 10})
+        self.assertRaises(TypeError, sql.compose, "select %(x)s;", [10])
+
     def test_must_be_adaptable(self):
         class Foo(object):
             pass