diff --git a/jedi/evaluate/names.py b/jedi/evaluate/names.py
index 22b9db79..f7e6b11a 100644
--- a/jedi/evaluate/names.py
+++ b/jedi/evaluate/names.py
@@ -176,6 +176,15 @@ class ParamName(ParamNameInterface, AbstractTreeName):
     def _get_param_node(self):
         return search_ancestor(self.tree_name, 'param')
 
+    @property
+    def string_name(self):
+        name = self.tree_name.value
+        if name.startswith('__'):
+            # Params starting with __ are an equivalent to positional only
+            # variables in typeshed.
+            name = name[2:]
+        return name
+
     def get_kind(self):
         tree_param = self._get_param_node()
         if tree_param.star_count == 1:  # *args
@@ -205,12 +214,7 @@ class ParamName(ParamNameInterface, AbstractTreeName):
         return Parameter.POSITIONAL_OR_KEYWORD
 
     def to_string(self):
-        name = self.string_name
-        if name.startswith('__'):
-            # Params starting with __ are an equivalent to positional only
-            # variables in typeshed.
-            name = name[2:]
-        output = self._kind_string() + name
+        output = self._kind_string() + self.string_name
         param_node = self._get_param_node()
         if param_node.annotation is not None:
             output += ': ' + param_node.annotation.get_code(include_prefix=False)
diff --git a/test/test_api/test_call_signatures.py b/test/test_api/test_call_signatures.py
index 75b4c8ac..c1bf1698 100644
--- a/test/test_api/test_call_signatures.py
+++ b/test/test_api/test_call_signatures.py
@@ -273,6 +273,13 @@ def test_int_params(Script):
     assert sig2.params[0].name == 'x'
 
 
+def test_pow_params(Script):
+    # See Github #1357.
+    for sig in Script('pow(').call_signatures():
+        param_names = [p.name for p in sig.params]
+        assert param_names in (['x', 'y'], ['x', 'y', 'z'])
+
+
 def test_param_name(Script):
     sigs = Script('open(something,').call_signatures()
     for sig in sigs: