diff --git a/apps/wpm/serializers.py b/apps/wpm/serializers.py
index 558d805d..89c45fed 100644
--- a/apps/wpm/serializers.py
+++ b/apps/wpm/serializers.py
@@ -884,8 +884,11 @@ class MlogbwCreateUpdateSerializer(CustomModelSerializer):
         if ftest_data:
             mlogbw = self.save_ftest(mlogbw, ftest_data)
         elif ftest_data is None:
-            if mlogbw.ftest:
-                mlogbw.ftest.delete()
+            ftest = mlogbw.ftest
+            if ftest:
+                mlogbw.ftest = None
+                mlogbw.save()
+                ftest.delete()
         return mlogbw
 
 class MlogbOutUpdateSerializer(CustomModelSerializer):