diff --git a/Project.toml b/Project.toml
index 92ca552..ff7f072 100644
--- a/Project.toml
+++ b/Project.toml
@@ -15,7 +15,7 @@ Reexport = "189a3867-3050-52da-a836-e630ba90ab69"
 [compat]
 HerbConstraints = "0.4"
 HerbCore = "0.3"
-HerbGrammar = "0.5"
+HerbGrammar = "0.5, 0.6"
 HerbInterpret = "0.1.2"
 HerbSearch = "0.4"
 HerbSpecification = "0.2"