diff --git a/main/src/com/google/refine/model/ColumnModel.java b/main/src/com/google/refine/model/ColumnModel.java
index 4bf1fb598..f310d3807 100644
--- a/main/src/com/google/refine/model/ColumnModel.java
+++ b/main/src/com/google/refine/model/ColumnModel.java
@@ -283,12 +283,17 @@ public class ColumnModel implements Jsonizable {
         _nameToColumn = new HashMap<String, Column>();
         _cellIndexToColumn = new HashMap<Integer, Column>();
         _columnNames = new ArrayList<String>();
-        
+        int maxCellIndex = -1;
         for (Column column : columns) {
             _nameToColumn.put(column.getName(), column);
-            _cellIndexToColumn.put(column.getCellIndex(), column);
+            int cidx = column.getCellIndex();
+            if (cidx > maxCellIndex) {
+                maxCellIndex = cidx;
+            }
+            _cellIndexToColumn.put(cidx, column);
             _columnNames.add(column.getName());
         }
+        _maxCellIndex = maxCellIndex;
     }
     
     /**