diff --git a/geomagio/residual/Measurement.py b/geomagio/residual/Measurement.py
index c8807e51cc1b08c947ea326adc7fe12e743440e0..c8b44707cf924251de0e7ffa984c1a5cd3cfbc40 100644
--- a/geomagio/residual/Measurement.py
+++ b/geomagio/residual/Measurement.py
@@ -22,4 +22,4 @@ class Measurement(BaseModel):
     angle: float = 0
     residual: float = 0
     time: Optional[UTCDateTime] = None
-    mask: bool = None
+    mask: bool = False