diff --git a/jedi/evaluate_representation.py b/jedi/evaluate_representation.py
index e294e1d1..74ce5b46 100644
--- a/jedi/evaluate_representation.py
+++ b/jedi/evaluate_representation.py
@@ -169,7 +169,7 @@ class Instance(use_metaclass(cache.CachedMetaClass, Executable)):
 
     def __getattr__(self, name):
         if name not in ['start_pos', 'end_pos', 'name', 'get_imports',
-                                                        'docstr', 'asserts']:
+                'doc', 'docstr', 'asserts']:
             raise AttributeError("Instance %s: Don't touch this (%s)!"
                                     % (self, name))
         return getattr(self.base, name)
diff --git a/test/regression.py b/test/regression.py
index a7cdc12f..67b1e7d3 100755
--- a/test/regression.py
+++ b/test/regression.py
@@ -90,6 +90,15 @@ class TestRegression(TestBase):
         if not is_py25:
             assert len(r[0].doc) > 100
 
+    def test_function_call_signature(self):
+        defs = self.definition("""
+        def f(x, y=1, z='a'):
+            pass
+        f""")
+        doc = defs[0].doc
+        doc = defs[0].doc  # removing this line won't work
+        assert "f(x, y = 1, z = 'a')" in doc
+
     def test_definition_at_zero(self):
         assert self.definition("a", (1, 1)) == []
         s = self.definition("str", (1, 1))