diff --git a/cli/app/undeploy.go b/cli/app/undeploy.go
index e5861994a..cbf8a7704 100644
--- a/cli/app/undeploy.go
+++ b/cli/app/undeploy.go
@@ -87,9 +87,12 @@ var appUndeployCommand = cli.Command{
 	Usage:        "Undeploy an app",
 	BashComplete: autocomplete.AppNameComplete,
 	Description: `
-This does not destroy any of the application data. However, you should remain
-vigilant, as your swarm installation will consider any previously attached
-volumes as eligible for pruning once undeployed.
+This does not destroy any of the application data.
+
+However, you should remain vigilant, as your swarm installation will consider
+any previously attached volumes as eligible for pruning once undeployed.
+
+Passing "-p/--prune" does not remove those volumes.
 `,
 	Action: func(c *cli.Context) error {
 		app := internal.ValidateApp(c)