diff --git a/_pytest/python.py b/_pytest/python.py
index 89be2598a..544055ec9 100644
--- a/_pytest/python.py
+++ b/_pytest/python.py
@@ -1841,7 +1841,13 @@ def getfuncargnames(function, startindex=None):
     if startindex is None:
         startindex = inspect.ismethod(function) and 1 or 0
     if realfunction != function:
-        startindex += len(getattr(function, "patchings", []))
+        mock = sys.modules.get('mock')
+        if mock is not None:
+            for patching in getattr(function, "patchings", []):
+                if not patching.attribute_name and patching.new is mock.DEFAULT:
+                    startindex += 1
+        else:
+            startindex += len(getattr(function, "patchings", []))
         function = realfunction
     argnames = inspect.getargs(py.code.getrawcode(function))[0]
     defaults = getattr(function, 'func_defaults',
diff --git a/testing/python/integration.py b/testing/python/integration.py
index 6fbf44572..e070b4398 100644
--- a/testing/python/integration.py
+++ b/testing/python/integration.py
@@ -124,8 +124,11 @@ class TestMockDecoration:
                 def test_hello(self, abspath):
                     os.path.abspath("hello")
                     abspath.assert_any_call("hello")
+            def mock_basename(path):
+                return "mock_basename"
             @mock.patch("os.path.abspath")
             @mock.patch("os.path.normpath")
+            @mock.patch("os.path.basename",new=mock_basename)
             def test_someting(normpath, abspath, tmpdir):
                 abspath.return_value = "this"
                 os.path.normpath(os.path.abspath("hello"))