diff --git a/jedi/api/classes.py b/jedi/api/classes.py
index 00eefa70..7bd1e336 100644
--- a/jedi/api/classes.py
+++ b/jedi/api/classes.py
@@ -326,7 +326,7 @@ class BaseDefinition(object):
             raise AttributeError()
         followed = followed[0]  # only check the first one.
 
-        if followed.isinstance(er.Function):
+        if followed.type == 'funcdef':
             if isinstance(followed, er.InstanceElement):
                 params = followed.params[1:]
             else:
diff --git a/jedi/evaluate/compiled/__init__.py b/jedi/evaluate/compiled/__init__.py
index bf62c643..0f5babfa 100644
--- a/jedi/evaluate/compiled/__init__.py
+++ b/jedi/evaluate/compiled/__init__.py
@@ -85,6 +85,8 @@ class CompiledObject(Base):
     def params(self):
         params_str, ret = self._parse_function_doc()
         tokens = params_str.split(',')
+        if inspect.ismethoddescriptor(self._cls().obj):
+            tokens.insert(0, 'self')
         params = []
         for p in tokens:
             parts = [FakeName(part) for part in p.strip().split('=')]
diff --git a/test/test_api/test_call_signatures.py b/test/test_api/test_call_signatures.py
index 5f56954f..0f968e94 100644
--- a/test/test_api/test_call_signatures.py
+++ b/test/test_api/test_call_signatures.py
@@ -230,6 +230,18 @@ class TestParams(TestCase):
         assert p[0].name in ['file', 'name']
         assert p[1].name == 'mode'
 
+    def test_builtins(self):
+        """
+        The self keyword should be visible even for builtins, if not
+        instantiated.
+        """
+        p = self.params('str.endswith(')
+        assert p[0].name == 'self'
+        assert p[1].name == 'suffix'
+        p = self.params('str.endswith(')
+        assert p[0].name == 'suffix'
+
+
 
 def test_signature_is_definition():
     """