diff --git a/reV/supply_curve/tech_mapping.py b/reV/supply_curve/tech_mapping.py
index 7c9b17da4..ba2f36611 100644
--- a/reV/supply_curve/tech_mapping.py
+++ b/reV/supply_curve/tech_mapping.py
@@ -329,8 +329,8 @@ def initialize_dataset(self, tm_dset, chunks=(128, 128)):
                     shape=self._excl_shape,
                     dtype=np.int32,
                     chunks=chunks,
+                    fillvalue=-1
                 )
-                f[tm_dset][:] = -1
 
             if self._dist_thresh:
                 f[tm_dset].attrs["distance_threshold"] = self._dist_thresh