@@ -340,8 +340,8 @@ def extension_add_subevent(self, code, subcode, evt, name = None):
         # extension dict maintained in the display object
         setattr(self.extension_event, name, (code,subcode))
 
-    def add_extension_error(self, code, err):
-        """add_extension_error(code, err)
+    def extension_add_error(self, code, err):
+        """extension_add_error(code, err)
 
         Add an extension error.  CODE is the numeric code, and ERR is
         the error class.
 
@@ -179,4 +179,4 @@ def init(disp, info):
 
     disp.extension_add_event(info.first_event + DamageNotifyCode, DamageNotify)
 
-    disp.add_extension_error(code=BadDamageCode, err=BadDamageError)
+    disp.extension_add_error(code=BadDamageCode, err=BadDamageError)
@@ -87,7 +87,7 @@ def test_cannot_add_existing_font_method(self):
         self.assertRaises(AssertionError, self.display.extension_add_method, "font", "__init__", lambda x: x)
 
     def test_can_add_extension_error(self):
-        self.display.add_extension_error(1, Xlib.error.XError)
+        self.display.extension_add_error(1, Xlib.error.XError)
         self.assertEqual(self.display.display.error_classes[1], Xlib.error.XError)
 
     def test_keycode_to_keysym_for_invalid_index(self):
Original file line number	Diff line number	Diff line change
`@@ -179,4 +179,4 @@ def init(disp, info):`
`179`	`179`
`180`	`180`	`disp.extension_add_event(info.first_event + DamageNotifyCode, DamageNotify)`
`181`	`181`
`182`		`- disp.add_extension_error(code=BadDamageCode, err=BadDamageError)`
	`182`	`+ disp.extension_add_error(code=BadDamageCode, err=BadDamageError)`