diff --git a/collector/pg_long_running_transactions.go b/collector/pg_long_running_transactions.go
index ffd89d5f0..1f0b76f9e 100644
--- a/collector/pg_long_running_transactions.go
+++ b/collector/pg_long_running_transactions.go
@@ -52,7 +52,7 @@ var (
 	longRunningTransactionsQuery = `
 	SELECT
 		COUNT(*) as transactions,
-   		MAX(EXTRACT(EPOCH FROM clock_timestamp())) AS oldest_timestamp_seconds
+		MIN(EXTRACT(EPOCH FROM xact_start)) AS oldest_timestamp_seconds
     FROM pg_catalog.pg_stat_activity
     WHERE state is distinct from 'idle' AND query not like 'autovacuum:%'
 	`