diff --git a/python/lsst/afw/image/_exposureSummaryStats.py b/python/lsst/afw/image/_exposureSummaryStats.py
index c2e85a5a6..2fc2a3e4a 100644
--- a/python/lsst/afw/image/_exposureSummaryStats.py
+++ b/python/lsst/afw/image/_exposureSummaryStats.py
@@ -81,6 +81,9 @@ class ExposureSummaryStats(Storable):
     skyBg: float = float('nan')
     """Average sky background (ADU)."""
 
+    skyLumpiness: float = float('nan')
+    """Unitless measure of spatial unevenness in the sky background."""
+
     skyNoise: float = float('nan')
     """Average sky noise (ADU)."""
 
@@ -301,6 +304,11 @@ def update_schema(cls, schema: Schema) -> None:
             doc="Average sky background (ADU)",
             units="adu",
         )
+        schema.addField(
+            "skyLumpiness",
+            type="F",
+            doc="Unitless measure of spatial unevenness in the sky background",
+        )
         schema.addField(
             "skyNoise",
             type="F",