diff --git a/lib/services/access_request.go b/lib/services/access_request.go
index 4ac9fe9aea31d..1e3ef0c8fb9de 100644
--- a/lib/services/access_request.go
+++ b/lib/services/access_request.go
@@ -121,7 +121,7 @@ func ValidateAccessRequestClusterNames(cg ClusterGetter, ar types.AccessRequest)
 	}
 	if len(invalidClusters) > 0 {
 		return trace.NotFound("access request contains invalid or unknown cluster names: %v",
-			strings.Join(invalidClusters, ", "))
+			strings.Join(apiutils.Deduplicate(invalidClusters), ", "))
 	}
 	return nil
 }