diff --git a/views.py b/views.py
index 00f4bfa..867e03d 100644
--- a/views.py
+++ b/views.py
@@ -209,7 +209,7 @@ class UpperLimitView(APIView):
         )
 
         annulus_pixels = Pixel.objects.filter(
-            hpid__in=annulus_pixel_list, survey__in=survey_numbers
+            hpid__in=annulus_pixel_list, survey__in=survey_numbers, contaminated=False
         )
 
         # check contamination
@@ -218,9 +218,14 @@ class UpperLimitView(APIView):
             or annulus_pixels.filter(contaminated=True).exists()
         )
 
-        if not source_pixels.exists() and not annulus_pixels.exists():
+        # exclude contaminated pixels from the background calculations
+        annulus_pixels = annulus_pixels.exclude(contaminated=True)
+
+        if not source_pixels.exists() or not annulus_pixels.exists():
             return Response(
-                {"detail": "No pixel data for the given survey selection."},
+                {
+                    "detail": "No background and/or source pixel data for the given survey selection."
+                },
                 status=status.HTTP_404_NOT_FOUND,
             )