diff --git a/src/main/cljc/org/domaindrivenarchitecture/activity_pub_poc/activitystreams2.cljc b/src/main/cljc/org/domaindrivenarchitecture/activity_pub_poc/activitystreams2.cljc
index b3554bc..6c92dd7 100644
--- a/src/main/cljc/org/domaindrivenarchitecture/activity_pub_poc/activitystreams2.cljc
+++ b/src/main/cljc/org/domaindrivenarchitecture/activity_pub_poc/activitystreams2.cljc
@@ -51,66 +51,72 @@
   (s/and 
    ::owl/ObjectProperty
    ::owl/Class
-   ::Object
-   ::Link))
+   (sh/seq-spec (s/and
+                 ::Object
+                 ::Link))))
 
 ;http://www.w3.org/ns/activitystreams#id
 (s/def ::id
   (s/and ::owl/DatatypeProperty
          ::owl/FunctionalProperty
          ::owl/DeprecatedProperty
-         ::xsd/anyURI))
+         (sh/seq-spec ::xsd/anyURI)))
 
 ;http://www.w3.org/ns/activitystreams#bcc
 (s/def ::bcc
   (s/and ::owl/ObjectProperty
-         ::Object
-         ::Link))
+         (sh/seq-spec (s/and
+                        ::Object
+                        ::Link))))
 
 ;http://www.w3.org/ns/activitystreams#bto
 (s/def ::bto
   (s/and ::owl/ObjectProperty
-         ::Object
-         ::Link))
+         (sh/seq-spec (s/and
+                        ::Object
+                        ::Link))))
 
 ;http://www.w3.org/ns/activitystreams#cc
 (s/def ::cc
   (s/and ::owl/ObjectProperty
-         ::Object
-         ::Link))
+         (sh/seq-spec (s/and
+                        ::Object
+                        ::Link))))
 
 ;http://www.w3.org/ns/activitystreams#to
 (s/def ::to
   (s/and ::owl/ObjectProperty
-         ::Object
-         ::Link))
+         (sh/seq-spec (s/and
+                        ::Object
+                        ::Link))))
 
 ;https://www.w3.org/TR/activitystreams-vocabulary/#dfn-type
 ;TODO: this can not be found in the ttl / namespace. Where is this exactly defined?
 (s/def ::type
-  (s/or
-   :single-value ::xsd/anyURI
-   :coll-of-values (s/+ ::xsd/anyURI)))
+  (sh/seq-spec ::xsd/anyURI))
 
 ;http://www.w3.org/ns/activitystreams#result
 (s/def ::result 
   (s/and 
    ::owl/ObjectProperty
-   ::Object
-   ::Link))
+   (sh/seq-spec (s/and
+                  ::Object
+                  ::Link))))
 
 ;http://www.w3.org/ns/activitystreams#object
 (s/def ::object 
   (s/and
    ::owl/ObjectProperty
    ::owl/Class
-   ::Object
-   ::Link))
+   (sh/seq-spec (s/and
+                  ::Object
+                  ::Link))))
 
 ;http://www.w3.org/ns/activitystreams#actor
 (s/def ::actor 
   (s/and
    ::owl/ObjectProperty
    ::owl/Class
-   ::Object
-   ::Link))
+   (sh/seq-spec (s/and
+                  ::Object
+                  ::Link))))
diff --git a/src/main/cljc/org/domaindrivenarchitecture/activity_pub_poc/spec_helper.cljc b/src/main/cljc/org/domaindrivenarchitecture/activity_pub_poc/spec_helper.cljc
index c4393fa..da44614 100644
--- a/src/main/cljc/org/domaindrivenarchitecture/activity_pub_poc/spec_helper.cljc
+++ b/src/main/cljc/org/domaindrivenarchitecture/activity_pub_poc/spec_helper.cljc
@@ -13,6 +13,14 @@
     :no-map #(not (map? %))
     :map spec)))
 
+(defn-spec seq-spec s/spec?
+  "Spec that applies only for map values."
+  [spec s/spec?]
+  (s/and
+   (s/or
+    :single-value spec
+    :coll-of-values (s/+ spec))))
+
 (defn-spec
   is-functional-property? boolean?
   "Checks whether spec is a FunctionalProperty."