diff --git a/README.md b/README.md
index add1ab3..bf0fa4b 100644
--- a/README.md
+++ b/README.md
@@ -73,7 +73,8 @@ OPTIONS:
     -t, --taddrs <t_addresses>    Numbe rof T addresses to generate [default: 0]
         --threads <threads>       Number of threads to use for the vanity address generator. Set this to the number of
                                   CPUs you have [default: 1]
-        --vanity <vanity>         Generate a vanity address with the given prefix
+        --vanity <vanity>         Generate a vanity address with the given prefix.
+                                  Note that ['b', 'i', 'o', '1'] are not allowed in addresses.
     -z, --zaddrs <z_addresses>    Number of Z addresses (Sapling) to generate [default: 1]
 
 ARGS: