diff --git a/libraries/tools/idl2k/src/main/antlr4/org/antlr/webidl/WebIDL.g4 b/libraries/tools/idl2k/src/main/antlr4/org/antlr/webidl/WebIDL.g4
index 4b9e381d93f..76839736132 100644
--- a/libraries/tools/idl2k/src/main/antlr4/org/antlr/webidl/WebIDL.g4
+++ b/libraries/tools/idl2k/src/main/antlr4/org/antlr/webidl/WebIDL.g4
@@ -470,6 +470,7 @@ nonAnyType
 	| 'Date' typeSuffix
 	| 'RegExp' typeSuffix
 	| 'DOMException' typeSuffix
+	| IDENTIFIER_WEBIDL '<' type '>' null_
 ;
 
 constType