diff --git a/django/contrib/gis/geos/prototypes/io.py b/django/contrib/gis/geos/prototypes/io.py
index 87aec30605..b2f544e5d6 100644
--- a/django/contrib/gis/geos/prototypes/io.py
+++ b/django/contrib/gis/geos/prototypes/io.py
@@ -233,29 +233,29 @@ class WKBWriter(IOBase):
     byteorder = property(_get_byteorder, _set_byteorder)
 
     # Property for getting/setting the output dimension.
-    def _get_outdim(self):
+    @property
+    def outdim(self):
         return wkb_writer_get_outdim(self.ptr)
 
-    def _set_outdim(self, new_dim):
+    @outdim.setter
+    def outdim(self, new_dim):
         if new_dim not in (2, 3):
             raise ValueError('WKB output dimension must be 2 or 3')
         wkb_writer_set_outdim(self.ptr, new_dim)
 
-    outdim = property(_get_outdim, _set_outdim)
-
     # Property for getting/setting the include srid flag.
-    def _get_include_srid(self):
+    @property
+    def srid(self):
         return bool(ord(wkb_writer_get_include_srid(self.ptr)))
 
-    def _set_include_srid(self, include):
+    @srid.setter
+    def srid(self, include):
         if include:
             flag = b'\x01'
         else:
             flag = b'\x00'
         wkb_writer_set_include_srid(self.ptr, flag)
 
-    srid = property(_get_include_srid, _set_include_srid)
-
 
 # `ThreadLocalIO` object holds instances of the WKT and WKB reader/writer
 # objects that are local to the thread.  The `GEOSGeometry` internals
diff --git a/tests/gis_tests/geos_tests/test_io.py b/tests/gis_tests/geos_tests/test_io.py
index 306824a4a8..e761cd61a3 100644
--- a/tests/gis_tests/geos_tests/test_io.py
+++ b/tests/gis_tests/geos_tests/test_io.py
@@ -101,9 +101,8 @@ class GEOSIOTest(SimpleTestCase):
 
         # Ensuring bad output dimensions are not accepted
         for bad_outdim in (-1, 0, 1, 4, 423, 'foo', None):
-            # Equivalent of `wkb_w.outdim = bad_outdim`
             with self.assertRaises(ValueError):
-                wkb_w._set_outdim(bad_outdim)
+                wkb_w.outdim = bad_outdim
 
         # Now setting the output dimensions to be 3
         wkb_w.outdim = 3