diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Rows/XLRow.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Rows/XLRow.cs
index 4e6fb31..bf94934 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Rows/XLRow.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Rows/XLRow.cs
@@ -417,8 +417,8 @@
             get { return IsReference ? Worksheet.Internals.RowsCollection[RowNumber()].OutlineLevel : _outlineLevel; }
             set
             {
-                if (value < 1 || value > 8)
-                    throw new ArgumentOutOfRangeException("value", "Outline level must be between 1 and 8.");
+                if (value < 0 || value > 8)
+                    throw new ArgumentOutOfRangeException("value", "Outline level must be between 0 and 8.");
 
                 if (IsReference)
                     Worksheet.Internals.RowsCollection[RowNumber()].OutlineLevel = value;
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
index 6bd162e..fbf3684 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
@@ -979,7 +979,8 @@
 
         public Int32 GetMaxColumnOutline()
         {
-            return _columnOutlineCount.Count == 0 ? 0 : _columnOutlineCount.Where(kp => kp.Value > 0).Max(kp => kp.Key);
+            var list = _columnOutlineCount.Where(kp => kp.Value > 0).ToList();
+            return list.Count == 0 ? 0 : list.Max(kp => kp.Key);
         }
 
         public void IncrementRowOutline(Int32 level)
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Columns/ColumnsTests.cs b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Columns/ColumnsTests.cs
index a245c2c..9eabebb 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Columns/ColumnsTests.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Columns/ColumnsTests.cs
@@ -207,5 +207,14 @@
 
             Assert.AreEqual("X", column2.Cell(2).GetString());
         }
+
+        [TestMethod]
+        public void UngroupFromAll()
+        {
+            var ws = new XLWorkbook().AddWorksheet("Sheet1");
+            ws.Columns(1, 2).Group();
+            ws.Columns(1, 2).Ungroup(true);
+
+        }
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Rows/RowsTests.cs b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Rows/RowsTests.cs
index fdbe11c..79b4e57 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Rows/RowsTests.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/Rows/RowsTests.cs
@@ -207,5 +207,15 @@
 
             Assert.AreEqual("X", row2.Cell(2).GetString());
         }
+
+
+        [TestMethod]
+        public void UngroupFromAll()
+        {
+            var ws = new XLWorkbook().AddWorksheet("Sheet1");
+            ws.Rows(1,2).Group();
+            ws.Rows(1,2).Ungroup(true);
+            
+        }
     }
 }