diff --git a/jedi/inference/signature.py b/jedi/inference/signature.py
index ecf43862..7837fb88 100644
--- a/jedi/inference/signature.py
+++ b/jedi/inference/signature.py
@@ -131,7 +131,6 @@ class BuiltinSignature(AbstractSignature):
         return self.value
 
     def bind(self, value):
-        assert not self.is_bound
         return BuiltinSignature(value, self._return_string, is_bound=True)
 
 
diff --git a/test/test_inference/test_docstring.py b/test/test_inference/test_docstring.py
index 83e86818..a0ec9b7a 100644
--- a/test/test_inference/test_docstring.py
+++ b/test/test_inference/test_docstring.py
@@ -414,3 +414,13 @@ def test_decorator(Script):
 
     d, = Script(code).goto_definitions()
     assert d.docstring(raw=True) == 'Nice docstring'
+
+
+def test_basic_str_init_signature(Script, disable_typeshed):
+    # See GH #1414 and GH #1426
+    code = dedent('''
+        class Foo(str):
+            pass
+        Foo(''')
+    c, = Script(code).call_signatures()
+    assert c.name == 'Foo'