diff --git a/shamir_mnemonic/cli.py b/shamir_mnemonic/cli.py
index bb7f05a..5a75ea4 100644
--- a/shamir_mnemonic/cli.py
+++ b/shamir_mnemonic/cli.py
@@ -34,7 +34,11 @@ def cli() -> None:
     help="Number of groups required for recovery in the custom scheme.",
 )
 @click.option(
-    "-x", "--extendable", type=bool, default=True, help="Extendable backup flag."
+    "-x/-X",
+    "--extendable/--no-extendable",
+    is_flag=True,
+    default=True,
+    help="Extendable backup flag.",
 )
 @click.option("-E", "--exponent", type=int, default=0, help="Iteration exponent.")
 @click.option(