diff --git a/trestle/tasks/cis_xlsx_to_oscal_catalog.py b/trestle/tasks/cis_xlsx_to_oscal_catalog.py
index 531c69c0b..a9ff699ff 100644
--- a/trestle/tasks/cis_xlsx_to_oscal_catalog.py
+++ b/trestle/tasks/cis_xlsx_to_oscal_catalog.py
@@ -81,7 +81,7 @@ def _translate(self, name: str) -> str:
     def _mapper(self) -> None:
         """Map columns heading names to column numbers."""
         self._col_name_to_number = {}
-        cols = self._work_sheet.max_column
+        cols = self._work_sheet.max_column + 1
         row = 1
         for col in range(row, cols):
             cell = self._work_sheet.cell(row, col)