diff --git a/spacy/errors.py b/spacy/errors.py
index 2b67aa87b..608305a06 100644
--- a/spacy/errors.py
+++ b/spacy/errors.py
@@ -212,7 +212,6 @@ class Warnings(metaclass=ErrorsWithCodes):
     W121 = ("Attempting to trace non-existent method '{method}' in pipe '{pipe}'")
     W122 = ("Couldn't trace method '{method}' in pipe '{pipe}'. This can happen if the pipe class "
             "is a Cython extension type.")
-    W400 = ("Activation '{activation}' is unknown for pipe '{pipe_name}'")
 
 
 class Errors(metaclass=ErrorsWithCodes):