diff --git a/mosaic/descriptor.py b/mosaic/descriptor.py
index 6bc9b87..5922699 100644
--- a/mosaic/descriptor.py
+++ b/mosaic/descriptor.py
@@ -83,7 +83,7 @@ def fix_outofbounds_indices(ds, array_name):
             # get mask of where index is out bounds
             mask = ds[array_name] == maxSize
             # where index is out of bounds, set to invalid (i.e. -1)
-            ds[array_name] = xr.where(mask, 1, ds[array_name])
+            ds[array_name] = xr.where(mask, -1, ds[array_name])
 
             return ds