diff --git a/webapi/src/main/scala/org/knora/webapi/responders/v2/OntologyResponderV2.scala b/webapi/src/main/scala/org/knora/webapi/responders/v2/OntologyResponderV2.scala
index 0506b80113..e5c7277a14 100644
--- a/webapi/src/main/scala/org/knora/webapi/responders/v2/OntologyResponderV2.scala
+++ b/webapi/src/main/scala/org/knora/webapi/responders/v2/OntologyResponderV2.scala
@@ -1403,12 +1403,15 @@ class OntologyResponderV2(responderData: ResponderData) extends Responder(respon
 
         currentTime: Instant = Instant.now
 
+        cardinalitiesToAdd: Map[SmartIri, KnoraCardinalityInfo] =
+          newInternalClassDefWithLinkValueProps.directCardinalities -- existingClassDef.directCardinalities.keySet
+
         updateSparql = org.knora.webapi.messages.twirl.queries.sparql.v2.txt
                          .addCardinalitiesToClass(
                            ontologyNamedGraphIri = internalOntologyIri,
                            ontologyIri = internalOntologyIri,
                            classIri = internalClassIri,
-                           cardinalitiesToAdd = newInternalClassDefWithLinkValueProps.directCardinalities,
+                           cardinalitiesToAdd = cardinalitiesToAdd,
                            lastModificationDate = addCardinalitiesRequest.lastModificationDate,
                            currentTime = currentTime
                          )
diff --git a/webapi/src/test/scala/org/knora/webapi/responders/v2/ontology/AddCardinalitiesToClassSpec.scala b/webapi/src/test/scala/org/knora/webapi/responders/v2/ontology/AddCardinalitiesToClassSpec.scala
new file mode 100644
index 0000000000..20994ef135
--- /dev/null
+++ b/webapi/src/test/scala/org/knora/webapi/responders/v2/ontology/AddCardinalitiesToClassSpec.scala
@@ -0,0 +1,111 @@
+/*
+ * Copyright © 2021 - 2022 Swiss National Data and Service Center for the Humanities and/or DaSCH Service Platform contributors.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.knora.webapi.responders.v2.ontology
+
+import akka.util.Timeout
+import org.knora.webapi.ApiV2Complex
+import org.knora.webapi.CoreSpec
+import org.knora.webapi.messages.IriConversions._
+import org.knora.webapi.messages.OntologyConstants
+import org.knora.webapi.messages.SmartIri
+import org.knora.webapi.messages.StringFormatter
+import org.knora.webapi.messages.store.triplestoremessages.RdfDataObject
+import org.knora.webapi.messages.store.triplestoremessages.SmartIriLiteralV2
+import org.knora.webapi.messages.store.triplestoremessages.SparqlSelectRequest
+import org.knora.webapi.messages.util.rdf.SparqlSelectResult
+import org.knora.webapi.messages.v2.responder.ontologymessages.AddCardinalitiesToClassRequestV2
+import org.knora.webapi.messages.v2.responder.ontologymessages.Cardinality
+import org.knora.webapi.messages.v2.responder.ontologymessages.ClassInfoContentV2
+import org.knora.webapi.messages.v2.responder.ontologymessages.ClassesGetRequestV2
+import org.knora.webapi.messages.v2.responder.ontologymessages.OntologyMetadataGetByIriRequestV2
+import org.knora.webapi.messages.v2.responder.ontologymessages.PredicateInfoV2
+import org.knora.webapi.messages.v2.responder.ontologymessages.ReadOntologyMetadataV2
+import org.knora.webapi.messages.v2.responder.ontologymessages.ReadOntologyV2
+import org.knora.webapi.sharedtestdata.SharedTestDataADM
+
+import java.time.Instant
+import java.util.UUID
+import scala.concurrent.duration._
+
+/**
+ * This spec is used to test [[org.knora.webapi.responders.v2.ontology.Cardinalities]].
+ */
+class AddCardinalitiesToClassSpec extends CoreSpec {
+
+  private implicit val stringFormatter: StringFormatter = StringFormatter.getGeneralInstance
+  private implicit val timeout                          = 10.seconds
+  private val freeTestOntology = RdfDataObject(
+    path = "test_data/ontologies/freetest-onto.ttl",
+    name = "http://www.knora.org/ontology/0001/freetest"
+  )
+  override lazy val rdfDataObjects: List[RdfDataObject] = List(freeTestOntology)
+
+  private def getCardinalityCountFromTriplestore(classIri: SmartIri, propertyIri: SmartIri) = {
+    val sparqlCountQuery =
+      s"""|PREFIX owl: <http://www.w3.org/2002/07/owl#>
+          |PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
+          |
+          |SELECT (count(?blanknode) as ?count)
+          |WHERE {
+          |  <$classIri> rdfs:subClassOf ?blanknode 
+          |  FILTER isBlank(?blanknode)
+          |  ?blanknode owl:onProperty <$propertyIri>
+          |}
+          |""".stripMargin
+    appActor ! SparqlSelectRequest(sparqlCountQuery)
+    val sparqlCountResponseInitial = expectMsgType[SparqlSelectResult]
+    sparqlCountResponseInitial.results.bindings.head.rowMap.values.head
+  }
+
+  val freetestOntologyIri: SmartIri = "http://0.0.0.0:3333/ontology/0001/freetest/v2".toSmartIri
+
+  "The ontology responder" should {
+    "add a cardinality to a class without duplicating all existing cardinalities in the triplestore" in {
+
+      val user           = SharedTestDataADM.anythingAdminUser
+      val classIri       = "http://www.knora.org/ontology/0001/freetest#Book".toSmartIri
+      val propertyIri    = "http://www.knora.org/ontology/0001/freetest#hasAuthor".toSmartIri
+      val newPropertyIri = "http://www.knora.org/ontology/0001/freetest#hasName".toSmartIri
+
+      // check ontology first
+      appActor ! OntologyMetadataGetByIriRequestV2(ontologyIris = Set(freetestOntologyIri), requestingUser = user)
+      val ontologyMetadata = expectMsgType[ReadOntologyMetadataV2]
+      val ontologyLastModificationDate = ontologyMetadata.ontologies.head.lastModificationDate
+        .getOrElse(throw new AssertionError("Ontology does not have a LastModificationDate"))
+
+      // assert that the cardinality for `:hasAuthor` is only once in the triplestore
+      val countInitial = getCardinalityCountFromTriplestore(classIri, propertyIri)
+      assert(countInitial == "1")
+
+      // add an additional cardinality to the class
+      val addCardinalitiesRequest = AddCardinalitiesToClassRequestV2(
+        classInfoContent = ClassInfoContentV2(
+          classIri = classIri.toOntologySchema(ApiV2Complex),
+          ontologySchema = ApiV2Complex,
+          predicates = Map(
+            OntologyConstants.Rdf.Type.toSmartIri -> PredicateInfoV2(
+              predicateIri = OntologyConstants.Rdf.Type.toSmartIri,
+              objects = Vector(SmartIriLiteralV2(value = OntologyConstants.Owl.Class.toSmartIri))
+            )
+          ),
+          directCardinalities =
+            Map(newPropertyIri -> Cardinality.KnoraCardinalityInfo(cardinality = Cardinality.MayHaveOne))
+        ),
+        lastModificationDate = ontologyLastModificationDate,
+        apiRequestID = UUID.randomUUID,
+        requestingUser = user
+      )
+      appActor ! addCardinalitiesRequest
+      val addCardinalitiesResponse = expectMsgType[ReadOntologyV2]
+
+      // assert that the cardinalities for `:hasAuthor` and `:hasName` is still only once in the triplestore
+      val countAfterwards = getCardinalityCountFromTriplestore(classIri, propertyIri)
+      assert(countAfterwards == "1")
+      val countNewProperty = getCardinalityCountFromTriplestore(classIri, newPropertyIri)
+      assert(countNewProperty == "1")
+    }
+  }
+}