diff --git a/vm-image-spec.yaml b/vm-image-spec.yaml
index 2767710bad..7d005c7139 100644
--- a/vm-image-spec.yaml
+++ b/vm-image-spec.yaml
@@ -277,8 +277,12 @@ files:
         help: 'Bytes between received and replayed LSN'
         key_labels:
         values: [replication_delay_bytes]
+        # We use a GREATEST call here because this calculation can be negative.
+        # The calculation is not atomic, meaning after we've gotten the receive
+        # LSN, the replay LSN may have advanced past the receive LSN we
+        # are using for the calculation.
         query: |
-          SELECT pg_wal_lsn_diff(pg_last_wal_receive_lsn(), pg_last_wal_replay_lsn()) AS replication_delay_bytes;
+          SELECT GREATEST(0, pg_wal_lsn_diff(pg_last_wal_receive_lsn(), pg_last_wal_replay_lsn())) AS replication_delay_bytes;
 
       - metric_name: replication_delay_seconds
         type: gauge