diff --git a/redbot/cogs/mod/mutes.py b/redbot/cogs/mod/mutes.py
index 5ee6126cc..14cd2037a 100644
--- a/redbot/cogs/mod/mutes.py
+++ b/redbot/cogs/mod/mutes.py
@@ -22,6 +22,7 @@ mute_unmute_issues = {
         "permission and the user I'm muting must be "
         "lower than myself in the role hierarchy."
     ),
+    "left_guild": _("The user has left the server while we're applying a overwrite.")
 }
 _ = T_
 
@@ -422,6 +423,8 @@ class MuteMixin(MixinMeta):
             await channel.set_permissions(user, overwrite=overwrites, reason=reason)
         except discord.Forbidden:
             return False, _(mute_unmute_issues["permissions_issue"])
+        except discord.NotFound:
+            return False, _(mute_unmute_issues["left_guild"])
         else:
             await self.settings.member(user).set_raw(
                 "perms_cache", str(channel.id), value=old_overs
@@ -460,6 +463,8 @@ class MuteMixin(MixinMeta):
                 await channel.set_permissions(user, overwrite=overwrites, reason=reason)
         except discord.Forbidden:
             return False, _(mute_unmute_issues["permissions_issue"])
+        except discord.NotFound:
+            return False, _(mute_unmute_issues["left_guild"])
         else:
             await self.settings.member(user).clear_raw("perms_cache", str(channel.id))
             return True, None