diff --git a/lib/cdc/mongo/debezium.go b/lib/cdc/mongo/debezium.go
index 72850d766..c5f07b451 100644
--- a/lib/cdc/mongo/debezium.go
+++ b/lib/cdc/mongo/debezium.go
@@ -3,6 +3,7 @@ package mongo
 import (
 	"encoding/json"
 	"fmt"
+	"log/slog"
 	"reflect"
 	"time"
 
@@ -175,8 +176,16 @@ func (s *SchemaEventPayload) GetData(pkMap map[string]any, tc kafkalib.TopicConf
 		retMap = s.Payload.afterMap
 		// We need this because there's an edge case with Debezium
 		// Where _id gets rewritten as id in the partition key.
-		for k, v := range pkMap {
-			retMap[k] = v
+		for key, value := range pkMap {
+			retData, isOk := retMap[key]
+			if !isOk {
+				slog.Warn("key not found in retMap", slog.String("key", key), slog.Any("retData", retData))
+			} else if retData != value {
+				slog.Warn("value mismatch", slog.String("key", key), slog.Any("value", value), slog.Any("retData", retData))
+			}
+
+			// TODO: Preserve behavior.
+			retMap[key] = value
 		}
 
 		retMap[constants.DeleteColumnMarker] = false