diff --git a/internal/netbox/inventory/add_items.go b/internal/netbox/inventory/add_items.go
index 52fae732..c84d77af 100644
--- a/internal/netbox/inventory/add_items.go
+++ b/internal/netbox/inventory/add_items.go
@@ -46,6 +46,8 @@ func (nbi *NetboxInventory) AddTag(ctx context.Context, newTag *objects.Tag) (*o
 // AddContact adds a contact to the local netbox inventory.
 func (nbi *NetboxInventory) AddTenant(ctx context.Context, newTenant *objects.Tenant) (*objects.Tenant, error) {
 	newTenant.Tags = append(newTenant.Tags, nbi.SsotTag)
+	nbi.TenantsLock.Lock()
+	defer nbi.TenantsLock.Unlock()
 	if _, ok := nbi.TenantsIndexByName[newTenant.Name]; ok {
 		oldTenant := nbi.TenantsIndexByName[newTenant.Name]
 		diffMap, err := utils.JSONDiffMapExceptID(newTenant, oldTenant, false, nbi.SourcePriority)
@@ -247,20 +249,20 @@ func (nbi *NetboxInventory) AddContactAssignment(ctx context.Context, newCA *obj
 	return nbi.ContactAssignmentsIndexByContentTypeAndObjectIDAndContactIDAndRoleID[newCA.ContentType][newCA.ObjectID][newCA.Contact.ID][newCA.Role.ID], nil
 }
 
-func (nbi *NetboxInventory) AddCustomField(ctx context.Context, newCf *objects.CustomField) error {
+func (nbi *NetboxInventory) AddCustomField(ctx context.Context, newCf *objects.CustomField) (*objects.CustomField, error) {
 	nbi.CustomFieldsLock.Lock()
 	defer nbi.CustomFieldsLock.Unlock()
 	if _, ok := nbi.CustomFieldsIndexByName[newCf.Name]; ok {
 		oldCustomField := nbi.CustomFieldsIndexByName[newCf.Name]
 		diffMap, err := utils.JSONDiffMapExceptID(newCf, oldCustomField, false, nbi.SourcePriority)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		if len(diffMap) > 0 {
 			nbi.Logger.Debug(ctx, "Custom field ", newCf.Name, " already exists in Netbox but is out of date. Patching it... ")
 			patchedCf, err := service.Patch[objects.CustomField](ctx, nbi.NetboxAPI, oldCustomField.ID, diffMap)
 			if err != nil {
-				return err
+				return nil, err
 			}
 			nbi.CustomFieldsIndexByName[newCf.Name] = patchedCf
 		} else {
@@ -268,13 +270,13 @@ func (nbi *NetboxInventory) AddCustomField(ctx context.Context, newCf *objects.C
 		}
 	} else {
 		nbi.Logger.Debug(ctx, "Custom field ", newCf.Name, " does not exist in Netbox. Creating it...")
-		newCf, err := service.Create[objects.CustomField](ctx, nbi.NetboxAPI, newCf)
+		createdCf, err := service.Create[objects.CustomField](ctx, nbi.NetboxAPI, newCf)
 		if err != nil {
-			return err
+			return nil, err
 		}
-		nbi.CustomFieldsIndexByName[newCf.Name] = newCf
+		nbi.CustomFieldsIndexByName[createdCf.Name] = createdCf
 	}
-	return nil
+	return nbi.CustomFieldsIndexByName[newCf.Name], nil
 }
 
 func (nbi *NetboxInventory) AddClusterGroup(ctx context.Context, newCg *objects.ClusterGroup) (*objects.ClusterGroup, error) {
@@ -345,7 +347,7 @@ func (nbi *NetboxInventory) AddClusterType(ctx context.Context, newClusterType *
 	return newClusterType, nil
 }
 
-func (nbi *NetboxInventory) AddCluster(ctx context.Context, newCluster *objects.Cluster) error {
+func (nbi *NetboxInventory) AddCluster(ctx context.Context, newCluster *objects.Cluster) (*objects.Cluster, error) {
 	newCluster.Tags = append(newCluster.Tags, nbi.SsotTag)
 
 	nbi.ClustersLock.Lock()
@@ -356,13 +358,13 @@ func (nbi *NetboxInventory) AddCluster(ctx context.Context, newCluster *objects.
 		delete(nbi.OrphanManager[service.ClustersAPIPath], oldCluster.ID)
 		diffMap, err := utils.JSONDiffMapExceptID(newCluster, oldCluster, false, nbi.SourcePriority)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		if len(diffMap) > 0 {
 			nbi.Logger.Debug(ctx, "Cluster ", newCluster.Name, " already exists in Netbox but is out of date. Patching it...")
 			patchedCluster, err := service.Patch[objects.Cluster](ctx, nbi.NetboxAPI, oldCluster.ID, diffMap)
 			if err != nil {
-				return err
+				return nil, err
 			}
 			nbi.ClustersIndexByName[newCluster.Name] = patchedCluster
 		} else {
@@ -370,13 +372,13 @@ func (nbi *NetboxInventory) AddCluster(ctx context.Context, newCluster *objects.
 		}
 	} else {
 		nbi.Logger.Debug(ctx, "Cluster ", newCluster.Name, " does not exist in Netbox. Creating it...")
-		newCluster, err := service.Create[objects.Cluster](ctx, nbi.NetboxAPI, newCluster)
+		createdCluster, err := service.Create[objects.Cluster](ctx, nbi.NetboxAPI, newCluster)
 		if err != nil {
-			return err
+			return nil, err
 		}
-		nbi.ClustersIndexByName[newCluster.Name] = newCluster
+		nbi.ClustersIndexByName[createdCluster.Name] = createdCluster
 	}
-	return nil
+	return nbi.ClustersIndexByName[newCluster.Name], nil
 }
 
 func (nbi *NetboxInventory) AddDeviceRole(ctx context.Context, newDeviceRole *objects.DeviceRole) (*objects.DeviceRole, error) {
diff --git a/internal/netbox/inventory/init_items.go b/internal/netbox/inventory/init_items.go
index 637cbb2d..0b6a6644 100644
--- a/internal/netbox/inventory/init_items.go
+++ b/internal/netbox/inventory/init_items.go
@@ -301,7 +301,7 @@ func (nbi *NetboxInventory) InitCustomFields(ctx context.Context) error {
 // - host_memory
 // - sourceId - this is used to store the ID of the source object in Netbox (interfaces).
 func (nbi *NetboxInventory) InitSsotCustomFields(ctx context.Context) error {
-	err := nbi.AddCustomField(ctx, &objects.CustomField{
+	_, err := nbi.AddCustomField(ctx, &objects.CustomField{
 		Name:                  constants.CustomFieldSourceName,
 		Label:                 constants.CustomFieldSourceLabel,
 		Type:                  objects.CustomFieldTypeText,
@@ -316,7 +316,7 @@ func (nbi *NetboxInventory) InitSsotCustomFields(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	err = nbi.AddCustomField(ctx, &objects.CustomField{
+	_, err = nbi.AddCustomField(ctx, &objects.CustomField{
 		Name:                  constants.CustomFieldSourceIDName,
 		Label:                 constants.CustomFieldSourceIDLabel,
 		Type:                  objects.CustomFieldTypeText,
@@ -331,7 +331,7 @@ func (nbi *NetboxInventory) InitSsotCustomFields(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	err = nbi.AddCustomField(ctx, &objects.CustomField{
+	_, err = nbi.AddCustomField(ctx, &objects.CustomField{
 		Name:                  constants.CustomFieldHostCPUCoresName,
 		Label:                 constants.CustomFieldHostCPUCoresLabel,
 		Type:                  objects.CustomFieldTypeText,
@@ -346,7 +346,7 @@ func (nbi *NetboxInventory) InitSsotCustomFields(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	err = nbi.AddCustomField(ctx, &objects.CustomField{
+	_, err = nbi.AddCustomField(ctx, &objects.CustomField{
 		Name:                  constants.CustomFieldHostMemoryName,
 		Label:                 constants.CustomFieldHostMemoryLabel,
 		Type:                  objects.CustomFieldTypeText,
diff --git a/internal/netbox/inventory/inventory.go b/internal/netbox/inventory/inventory.go
index 5261c3de..b1bf30ab 100644
--- a/internal/netbox/inventory/inventory.go
+++ b/internal/netbox/inventory/inventory.go
@@ -73,6 +73,7 @@ type NetboxInventory struct {
 	IPAdressesIndexByAddress map[string]*objects.IPAddress
 
 	// We also store locks for all objects, so inventory can be updated by multiple parallel goroutines
+	TenantsLock            sync.Mutex
 	TagsLock               sync.Mutex
 	SitesLock              sync.Mutex
 	ContactRolesLock       sync.Mutex
diff --git a/internal/source/ovirt/ovirt_sync.go b/internal/source/ovirt/ovirt_sync.go
index a6c4dca6..732c9126 100644
--- a/internal/source/ovirt/ovirt_sync.go
+++ b/internal/source/ovirt/ovirt_sync.go
@@ -161,7 +161,7 @@ func (o *OVirtSource) syncClusters(nbi *inventory.NetboxInventory) error {
 			Site:   clusterSite,
 			Tenant: clusterTenant,
 		}
-		err := nbi.AddCluster(o.Ctx, nbCluster)
+		_, err := nbi.AddCluster(o.Ctx, nbCluster)
 		if err != nil {
 			return fmt.Errorf("failed to add oVirt cluster %s as Netbox cluster: %v", clusterName, err)
 		}
diff --git a/internal/source/vmware/vmware_sync.go b/internal/source/vmware/vmware_sync.go
index bb18023d..70d8045a 100644
--- a/internal/source/vmware/vmware_sync.go
+++ b/internal/source/vmware/vmware_sync.go
@@ -136,7 +136,7 @@ func (vc *VmwareSource) syncClusters(nbi *inventory.NetboxInventory) error {
 			Site:   clusterSite,
 			Tenant: clusterTenant,
 		}
-		err := nbi.AddCluster(vc.Ctx, nbCluster)
+		_, err := nbi.AddCluster(vc.Ctx, nbCluster)
 		if err != nil {
 			return fmt.Errorf("failed to add vmware cluster %s as Netbox cluster: %v", clusterName, err)
 		}
@@ -708,7 +708,7 @@ func (vc *VmwareSource) syncVms(nbi *inventory.NetboxInventory) error {
 					} else {
 						fieldName = utils.Alphanumeric(fieldName)
 						if _, ok := nbi.CustomFieldsIndexByName[fieldName]; !ok {
-							err := nbi.AddCustomField(vc.Ctx, &objects.CustomField{
+							_, err := nbi.AddCustomField(vc.Ctx, &objects.CustomField{
 								Name:                  fieldName,
 								Type:                  objects.CustomFieldTypeText,
 								CustomFieldUIVisible:  &objects.CustomFieldUIVisibleIfSet,