diff --git a/cmd-join-pane.c b/cmd-join-pane.c
index 3300498f..6eb0ea65 100644
--- a/cmd-join-pane.c
+++ b/cmd-join-pane.c
@@ -119,7 +119,7 @@ cmd_join_pane_exec(struct cmd *self, struct cmdq_item *item)
 		size = args_percentage_and_expand(args, 'l', 0, INT_MAX, curval,
 			   item, &cause);
 	} else if (args_has(args, 'p')) {
-		size = args_strtonum_and_expand(args, 'l', 0, 100, item,
+		size = args_strtonum_and_expand(args, 'p', 0, 100, item,
 			   &cause);
 		if (cause == NULL)
 			size = curval * size / 100;