diff --git a/ClosedXML/Excel/Cells/XLCell.cs b/ClosedXML/Excel/Cells/XLCell.cs
index f622f4a..e901eb3 100644
--- a/ClosedXML/Excel/Cells/XLCell.cs
+++ b/ClosedXML/Excel/Cells/XLCell.cs
@@ -225,6 +225,7 @@
         {
             FormulaA1 = String.Empty;
             _richText = null;
+            var style = GetStyleForRead();
             if (value is String || value is char)
             {
                 _cellValue = value.ToString();
@@ -236,13 +237,15 @@
             {
                 _cellValue = value.ToString();
                 _dataType = XLCellValues.TimeSpan;
-                Style.NumberFormat.NumberFormatId = 46;
+                if (style.NumberFormat.Format == String.Empty && style.NumberFormat.NumberFormatId == 0)
+                    Style.NumberFormat.NumberFormatId = 46;
             }
             else if (value is DateTime)
             {
                 _dataType = XLCellValues.DateTime;
                 var dtTest = (DateTime)Convert.ChangeType(value, typeof (DateTime));
-                Style.NumberFormat.NumberFormatId = dtTest.Date == dtTest ? 14 : 22;
+                if (style.NumberFormat.Format == String.Empty && style.NumberFormat.NumberFormatId == 0)
+                    Style.NumberFormat.NumberFormatId = dtTest.Date == dtTest ? 14 : 22;
 
                 _cellValue = dtTest.ToOADate().ToInvariantString();
             }
@@ -1671,7 +1674,6 @@
                             val = dtTest.ToOADate().ToInvariantString();
                         }
                     }
-
                 }
                 else if (Boolean.TryParse(val, out bTest))
                 {
diff --git a/ClosedXML_Tests/ClosedXML_Tests.csproj b/ClosedXML_Tests/ClosedXML_Tests.csproj
index 6f5439f..eabbee3 100644
--- a/ClosedXML_Tests/ClosedXML_Tests.csproj
+++ b/ClosedXML_Tests/ClosedXML_Tests.csproj
@@ -104,6 +104,7 @@
     <Compile Include="Excel\Ranges\InsertingRangesTests.cs" />
     <Compile Include="Excel\Rows\RowTests.cs" />
     <Compile Include="Excel\Styles\ColorTests.cs" />
+    <Compile Include="Excel\Styles\NumberFormatTests.cs" />
     <Compile Include="Excel\Styles\XLFillTests.cs" />
     <Compile Include="Excel\Tables\TablesTests.cs" />
     <Compile Include="Excel\Worksheets\XLWorksheetTests.cs" />
diff --git a/ClosedXML_Tests/Excel/Styles/NumberFormatTests.cs b/ClosedXML_Tests/Excel/Styles/NumberFormatTests.cs
new file mode 100644
index 0000000..cf3aa2b
--- /dev/null
+++ b/ClosedXML_Tests/Excel/Styles/NumberFormatTests.cs
@@ -0,0 +1,33 @@
+using ClosedXML.Excel;
+using NUnit.Framework;
+using System;
+using System.Data;
+using System.Linq;
+
+namespace ClosedXML_Tests.Excel
+{
+    public class NumberFormatTests
+    {
+        [Test]
+        public void PreserveCellFormat()
+        {
+            using (var wb = new XLWorkbook())
+            {
+                var ws = wb.AddWorksheet("Sheet1");
+                ws.Column(1).Style.NumberFormat.Format = "yy-MM-dd";
+
+                var table = new DataTable();
+                table.Columns.Add("Date", typeof(DateTime));
+
+                for (int i = 0; i < 10; i++)
+                {
+                    table.Rows.Add(new DateTime(2017, 1, 1).AddMonths(i));
+                }
+
+                ws.Cell("A1").InsertData(table.AsEnumerable());
+
+                Assert.AreEqual("yy-MM-dd", ws.Cell("A5").Style.DateFormat.Format);
+            }
+        }
+    }
+}