diff --git a/changelog.d/mod/3523.bugfix.rst b/changelog.d/mod/3523.bugfix.rst
new file mode 100644
index 000000000..e4bc1d9e2
--- /dev/null
+++ b/changelog.d/mod/3523.bugfix.rst
@@ -0,0 +1,2 @@
+Allow mentions in hackban and ban commands.
+Have the correct lower bound on length of a snowflake for the converter.
\ No newline at end of file
diff --git a/redbot/cogs/mod/converters.py b/redbot/cogs/mod/converters.py
index 8bed65c77..9bb9da7df 100644
--- a/redbot/cogs/mod/converters.py
+++ b/redbot/cogs/mod/converters.py
@@ -1,16 +1,20 @@
+import re
 from redbot.core.commands import Converter, BadArgument
 from redbot.core.i18n import Translator
 
 _ = Translator("Mod", __file__)
 
+_id_regex = re.compile(r"([0-9]{15,21})$")
+_mention_regex = re.compile(r"<@!?([0-9]{15,21})>$")
+
 
 class RawUserIds(Converter):
     async def convert(self, ctx, argument):
-        # This is for the hackban command, where we receive IDs that
+        # This is for the hackban and unban commands, where we receive IDs that
         # are most likely not in the guild.
-        # As long as it's numeric and long enough, it makes a good candidate
-        # to attempt a ban on
-        if argument.isnumeric() and len(argument) >= 17:
-            return int(argument)
+        # Mentions are supported, but most likely won't ever be in cache.
+
+        if match := _id_regex.match(argument) or _mention_regex.match(argument):
+            return int(match.group(1))
 
         raise BadArgument(_("{} doesn't look like a valid user ID.").format(argument))
diff --git a/redbot/cogs/mod/kickban.py b/redbot/cogs/mod/kickban.py
index 5b710f15e..8757f23f2 100644
--- a/redbot/cogs/mod/kickban.py
+++ b/redbot/cogs/mod/kickban.py
@@ -581,7 +581,7 @@ class KickBanMixin(MixinMeta):
     @commands.guild_only()
     @commands.bot_has_permissions(ban_members=True)
     @checks.admin_or_permissions(ban_members=True)
-    async def unban(self, ctx: commands.Context, user_id: int, *, reason: str = None):
+    async def unban(self, ctx: commands.Context, user_id: RawUserIds, *, reason: str = None):
         """Unban a user from this server.
 
         Requires specifying the target user's ID. To find this, you may either: