diff --git a/apps/wpm/serializers.py b/apps/wpm/serializers.py
index 8663e53a..ca29e518 100644
--- a/apps/wpm/serializers.py
+++ b/apps/wpm/serializers.py
@@ -591,14 +591,15 @@ class MlogbwCreateUpdateSerializer(CustomModelSerializer):
         return attrs
 
     def save_ftest(self, mlogbw, ftest_data):
-        if "id" not in ftest_data:
+        ftest = mlogbw.ftest
+        if not ftest:
             ftest_sr = FtestProcessSerializer(data=ftest_data)
             ftest = ftest_sr.create(ftest_data)
             mlogbw.ftest = ftest
             mlogbw.save()
         else:
             ftest_sr = FtestProcessSerializer()
-            ftest_sr.update(instance=Ftest.objects.get(id=ftest_data["id"]), validated_data=ftest_data)
+            ftest_sr.update(instance=ftest, validated_data=ftest_data)
         return mlogbw
 
     @transaction.atomic