diff --git a/pyhf/modifiers/shapesys.py b/pyhf/modifiers/shapesys.py
index 43e2c9d44b..67f42e55af 100644
--- a/pyhf/modifiers/shapesys.py
+++ b/pyhf/modifiers/shapesys.py
@@ -58,7 +58,7 @@ def __init__(self,shapesys_mods,pdfconfig,mega_mods):
                 zero_mask = summed_mask == 0
                 # then apply the mask
                 summed_mask[positive_mask] = inds
-                summed_mask[zero_mask] = 0
+                summed_mask[zero_mask] = len(self._parindices) - 1
                 access_rows.append(summed_mask.tolist())
             self._factor_access_indices = default_backend.tolist(default_backend.stack(access_rows))
             self.finalize(pdfconfig)
diff --git a/pyhf/modifiers/staterror.py b/pyhf/modifiers/staterror.py
index 8408c0b378..7e9c9751c0 100644
--- a/pyhf/modifiers/staterror.py
+++ b/pyhf/modifiers/staterror.py
@@ -55,7 +55,7 @@ def __init__(self,staterr_mods,pdfconfig,mega_mods):
                 zero_mask = summed_mask == 0
                 # then apply the mask
                 summed_mask[positive_mask] = inds
-                summed_mask[zero_mask] = 0
+                summed_mask[zero_mask] = len(self._parindices) - 1
                 access_rows.append(summed_mask.tolist())
             self._factor_access_indices = default_backend.tolist(default_backend.stack(access_rows))
             self.finalize(pdfconfig)