diff --git a/OpenXmlFormats/Spreadsheet/Sheet.cs b/OpenXmlFormats/Spreadsheet/Sheet.cs
index 3ea11b4c9..b51974cbf 100644
--- a/OpenXmlFormats/Spreadsheet/Sheet.cs
+++ b/OpenXmlFormats/Spreadsheet/Sheet.cs
@@ -7333,7 +7333,7 @@ public static CT_DataValidation Parse(XmlNode node, XmlNamespaceManager namespac
             }
             return ctObj;
         }
-
+        
         internal void Write(StreamWriter sw, string nodeName)
         {
             sw.Write(string.Format("<{0}", nodeName));
@@ -7352,9 +7352,9 @@ internal void Write(StreamWriter sw, string nodeName)
             XmlHelper.WriteAttribute(sw, "sqref", this.sqref);
             sw.Write(">");
             if (this.formula1 != null)
-                sw.Write(string.Format("<formula1><![CDATA[{0}]]></formula1>", this.formula1));
+                sw.Write(string.Format("<formula1><![CDATA[{0}]]></formula1>", XmlHelper.EncodeCDATAContent(this.formula1)));
             if (this.formula2 != null)
-                sw.Write(string.Format("<formula2><![CDATA[{0}]]></formula2>", this.formula2));
+                sw.Write(string.Format("<formula2><![CDATA[{0}]]></formula2>", XmlHelper.EncodeCDATAContent(this.formula2)));
 
             sw.Write(string.Format("</{0}>", nodeName));
         }
diff --git a/openxml4Net/Util/XmlHelper.cs b/openxml4Net/Util/XmlHelper.cs
index 91eae96df..70f668d91 100644
--- a/openxml4Net/Util/XmlHelper.cs
+++ b/openxml4Net/Util/XmlHelper.cs
@@ -314,6 +314,7 @@ public static string ExcelDecodeString(string t)
         }
 
         private static readonly char[] xmlEncodeCharsToReplace = { '&', '<', '>', '"' };
+        private static readonly char[] cdataEncodeCharsToReplace = { '&', '<', '>','\'' ,'"' };
 
         public static string EncodeXml(string xml)
         {
@@ -330,6 +331,22 @@ public static string EncodeXml(string xml)
                 .Replace("\"", "&quot;");//.Replace("'", "&apos;");
         }
 
+        public static string EncodeCDATAContent(string xml)
+        {
+            // quick check whether needed
+            if(xml.IndexOfAny(cdataEncodeCharsToReplace) == -1)
+            {
+                return xml;
+            }
+
+            return xml
+                .Replace("&", "&#38;")
+                .Replace("<", "&#60;")
+                .Replace(">", "&#62;")
+                .Replace("\"", "&#34;")
+                .Replace("'", "&#39;");
+        }
+
         public static void WriteAttribute(StreamWriter sw, string attributeName, bool value)
         {
             WriteAttribute(sw, attributeName, value, true);