diff --git a/db/migrations/008_packets_last_heard_index.sql b/db/migrations/008_packets_last_heard_index.sql
new file mode 100644
index 0000000..f8a4cec
--- /dev/null
+++ b/db/migrations/008_packets_last_heard_index.sql
@@ -0,0 +1,8 @@
+-- 008_packets_last_heard_index.sql
+--
+-- The packet list orders by last_heard_at but there was no index on it, so
+-- every page seq-scanned and sorted all packets (~2.8s per page on a 1.5M
+-- row table; 31ms with the index). Affordable to maintain now that presence
+-- coalescing keeps this column from being rewritten on every observation.
+
+CREATE INDEX idx_packets_last_heard ON packets(last_heard_at DESC);