diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/IXLRange.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/IXLRange.cs
index 6119b65..653fc81 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/IXLRange.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/IXLRange.cs
@@ -122,7 +122,7 @@
         }
         public static void Unmerge(this IXLRange range)
         {
-            range.MergedCells.Add(range.FirstCellAddress.ToString() + ":" + range.LastCellAddress.ToString());
+            range.MergedCells.Remove(range.FirstCellAddress.ToString() + ":" + range.LastCellAddress.ToString());
         }
 
         public static IXLRange FirstColumn(this IXLRange range)