diff --git a/src/flask/cli.py b/src/flask/cli.py
index 3fa65cfd01..a190e78872 100644
--- a/src/flask/cli.py
+++ b/src/flask/cli.py
@@ -858,7 +858,11 @@ def _validate_key(ctx: click.Context, param: click.Parameter, value: t.Any) -> t
         ctx.params["cert"] = cert, value
 
     else:
-        if cert and not (is_adhoc or is_context):
+        if (
+            cert is not None
+            and cert != click.utils.UNSET
+            and not (is_adhoc or is_context)
+        ):
             raise click.BadParameter('Required when using "--cert".', ctx, param)
 
     return value