diff --git a/src/_pytest/tmpdir.py b/src/_pytest/tmpdir.py
index 843c8ca37..4d109cc2b 100644
--- a/src/_pytest/tmpdir.py
+++ b/src/_pytest/tmpdir.py
@@ -31,7 +31,7 @@ class TempPathFactory(object):
         # using os.path.abspath() to get absolute path instead of resolve() as it
         # does not work the same in all platforms (see #4427)
         # Path.absolute() exists, but it is not public (see https://bugs.python.org/issue25012)
-        convert=attr.converters.optional(
+        converter=attr.converters.optional(
             lambda p: Path(os.path.abspath(six.text_type(p)))
         )
     )