diff --git a/src/wanijo/instance/domain.clj b/src/wanijo/instance/domain.clj
index 0db3923..f1ac656 100644
--- a/src/wanijo/instance/domain.clj
+++ b/src/wanijo/instance/domain.clj
@@ -7,7 +7,11 @@
 (spec/def ::created-at ::neo4j/date-str)
 (spec/def ::updated-at ::neo4j/date-str)
 (spec/def ::name (spec/and (complement empty?) string?))
-(spec/def ::value (some-fn string? boolean? nil? number?))
+(spec/def ::value
+  (spec/or :string string?
+           :bool boolean?
+           :nil nil?
+           :number number?))
 (spec/def ::instance_uuid ::neo4j/uuid)
 (spec/def ::attribute_uuid ::neo4j/uuid)