diff --git a/data/DiaSource.yaml b/data/DiaSource.yaml
index 7ea8bc39..9a397218 100644
--- a/data/DiaSource.yaml
+++ b/data/DiaSource.yaml
@@ -258,7 +258,7 @@ funcs:
     iyyPSF:
         functor: ConvertPixelSqToArcsecondsSq
         args:
-            - slot_PsfShape_xy
+            - slot_PsfShape_yy
             - base_LocalWcs_CDMatrix_1_1
             - base_LocalWcs_CDMatrix_1_2
             - base_LocalWcs_CDMatrix_2_1