diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9e79d6f..cfbc6e8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ Procedure when bumping the version number:
 - `bot::botrulez::FullHelp` now implements `bot::command::Command`
 - `bot::botrulez::Ping` now implements `bot::command::Command`
 - `bot::botrulez::ShortHelp` now implements `bot::command::Command`
+- `bot::instances::Instances::is_from_known_instance`
 
 ### Changed
 - Instances log to target `euphoxide::live::<name>`
diff --git a/src/bot/instances.rs b/src/bot/instances.rs
index f54ecf6..6607a70 100644
--- a/src/bot/instances.rs
+++ b/src/bot/instances.rs
@@ -2,7 +2,7 @@
 
 use std::collections::HashMap;
 
-use super::instance::{Instance, ServerConfig};
+use super::instance::{self, Instance, ServerConfig};
 
 /// A convenient way to keep a [`ServerConfig`] and some [`Instance`]s.
 pub struct Instances {
@@ -26,6 +26,18 @@ impl Instances {
         self.instances.values()
     }
 
+    /// Check if an event comes from an instance whose name is known.
+    ///
+    /// Assuming every instance has a unique name, events from unknown instances
+    /// should be discarded. This helps prevent "ghost instances" that were
+    /// stopped but haven't yet disconnected properly from influencing your
+    /// bot's state.
+    ///
+    /// The user is responsible for ensuring that instances' names are unique.
+    pub fn is_from_known_instance(&self, event: &instance::Event) -> bool {
+        self.instances.contains_key(&event.config().name)
+    }
+
     pub fn is_empty(&self) -> bool {
         self.instances.is_empty()
     }