diff --git a/cmd/kubeadm/app/cmd/options/generic.go b/cmd/kubeadm/app/cmd/options/generic.go
index 19436dcba9a..37536b6e520 100644
--- a/cmd/kubeadm/app/cmd/options/generic.go
+++ b/cmd/kubeadm/app/cmd/options/generic.go
@@ -54,6 +54,9 @@ func AddIgnorePreflightErrorsFlag(fs *pflag.FlagSet, ignorePreflightErrors *[]st
 
 // AddControlPlanExtraArgsFlags adds the ExtraArgs flags for control plane components
 func AddControlPlanExtraArgsFlags(fs *pflag.FlagSet, apiServerExtraArgs, controllerManagerExtraArgs, schedulerExtraArgs *map[string]string) {
+	// TODO: https://github.com/kubernetes/kubeadm/issues/1601
+	// Either deprecate these flags or handle duplicate keys.
+	// Currently the map[string]string returned by NewMapStringString() doesn't allow this.
 	fs.Var(cliflag.NewMapStringString(apiServerExtraArgs), APIServerExtraArgs, "A set of extra flags to pass to the API Server or override default ones in form of <flagname>=<value>")
 	fs.Var(cliflag.NewMapStringString(controllerManagerExtraArgs), ControllerManagerExtraArgs, "A set of extra flags to pass to the Controller Manager or override default ones in form of <flagname>=<value>")
 	fs.Var(cliflag.NewMapStringString(schedulerExtraArgs), SchedulerExtraArgs, "A set of extra flags to pass to the Scheduler or override default ones in form of <flagname>=<value>")