diff --git a/colorsynth/_colorsynth.py b/colorsynth/_colorsynth.py
index 012d293..4c0386d 100644
--- a/colorsynth/_colorsynth.py
+++ b/colorsynth/_colorsynth.py
@@ -71,6 +71,8 @@ def d65_standard_illuminant(
         x=wavelength,
         xp=wavl,
         fp=spd,
+        left=0,
+        right=0,
     )
     return result