--- WebIDL.py
+++ WebIDL.py
@@ -1357,7 +1357,8 @@ class IDLInterface(IDLObjectWithScope, IDLExposureMixins):
                   identifier == "ChromeOnly" or
                   identifier == "Unforgeable" or
                   identifier == "UnsafeInPrerendering" or
-                  identifier == "LegacyEventInit"):
+                  identifier == "LegacyEventInit" or
+                  identifier == "Abstract"):
                 # Known extended attributes that do not take values
                 if not attr.noArguments():
                     raise WebIDLError("[%s] must take no arguments" % identifier,