diff --git a/src/textual/dom.py b/src/textual/dom.py
index c6efd1c4f..12e8a9537 100644
--- a/src/textual/dom.py
+++ b/src/textual/dom.py
@@ -1123,7 +1123,8 @@ class DOMNode(MessagePump):
         """Replace all classes.
 
         Args:
-            A string contain space separated classes, or an iterable of class names.
+            classes: A string containing space separated classes, or an
+                iterable of class names.
 
         Returns:
             Self.