diff --git a/src/vault/euph.rs b/src/vault/euph.rs
index 1e9df1b..2517ba9 100644
--- a/src/vault/euph.rs
+++ b/src/vault/euph.rs
@@ -1224,10 +1224,9 @@ impl EuphRequest {
         let amount = conn
             .prepare(
                 "
-                SELECT COUNT(*)
-                FROM euph_msgs
+                SELECT amount
+                FROM euph_unseen_counts
                 WHERE room = ?
-                AND NOT seen
                 ",
             )?
             .query_row(params![room], |row| row.get(0))?;
diff --git a/src/vault/prepare.rs b/src/vault/prepare.rs
index 8f55fb0..8a9e67b 100644
--- a/src/vault/prepare.rs
+++ b/src/vault/prepare.rs
@@ -2,6 +2,7 @@ use rusqlite::Connection;
 
 pub fn prepare(conn: &mut Connection) -> rusqlite::Result<()> {
     println!("Opening vault");
+
     // This temporary table has no foreign key constraint on euph_rooms since
     // cross-schema constraints like that are not supported by SQLite.
     conn.execute_batch(
@@ -28,5 +29,73 @@ pub fn prepare(conn: &mut Connection) -> rusqlite::Result<()> {
             AND parents.id = euph_msgs.parent
         );
         ",
-    )
+    )?;
+
+    // Cache amount of unseen messages per room because counting them takes far
+    // too long. Uses triggers to move as much of the updating logic as possible
+    // into SQLite.
+    conn.execute_batch(
+        "
+        CREATE TEMPORARY TABLE euph_unseen_counts (
+            room   TEXT    NOT NULL,
+            amount INTEGER NOT NULL,
+
+            PRIMARY KEY (room)
+        ) STRICT;
+
+        -- There must be an entry for every existing room.
+        INSERT INTO euph_unseen_counts (room, amount)
+        SELECT room, 0
+        FROM euph_rooms;
+
+        INSERT OR REPLACE INTO euph_unseen_counts (room, amount)
+        SELECT room, COUNT(*)
+        FROM euph_msgs
+        WHERE NOT seen
+        GROUP BY room;
+
+        CREATE TEMPORARY TRIGGER euc_insert_room
+        AFTER INSERT ON euph_rooms
+        BEGIN
+            INSERT INTO euph_unseen_counts (room, amount)
+            VALUES (new.room, 0);
+        END;
+
+        CREATE TEMPORARY TRIGGER euc_delete_room
+        AFTER DELETE ON euph_rooms
+        BEGIN
+            DELETE FROM euph_unseen_counts
+            WHERE room = old.room;
+        END;
+
+        CREATE TEMPORARY TRIGGER euc_insert_msg
+        AFTER INSERT ON euph_msgs
+        WHEN NOT new.seen
+        BEGIN
+            UPDATE euph_unseen_counts
+            SET amount = amount + 1
+            WHERE room = new.room;
+        END;
+
+        CREATE TEMPORARY TRIGGER euc_update_msg
+        AFTER UPDATE OF seen ON euph_msgs
+        WHEN old.seen != new.seen
+        BEGIN
+            UPDATE euph_unseen_counts
+            SET amount = CASE WHEN new.seen THEN amount - 1 ELSE amount + 1 END
+            WHERE room = new.room;
+        END;
+
+        CREATE TEMPORARY TRIGGER euc_delete_msg
+        AFTER DELETE ON euph_msgs
+        WHEN NOT old.seen
+        BEGIN
+            UPDATE euph_unseen_counts
+            SET amount = amount - 1
+            WHERE room = old.room;
+        END;
+        ",
+    )?;
+
+    Ok(())
 }