diff --git a/ClosedXML/Excel/XLWorkbook.cs b/ClosedXML/Excel/XLWorkbook.cs
index ed6398f..9e86a67 100644
--- a/ClosedXML/Excel/XLWorkbook.cs
+++ b/ClosedXML/Excel/XLWorkbook.cs
@@ -1,14 +1,14 @@
+using ClosedXML.Excel.CalcEngine;
+using ClosedXML.Extensions;
+using DocumentFormat.OpenXml;
 using System;
 using System.Collections.Generic;
+using System.Data;
 using System.IO;
-using System.Security.AccessControl;
-using ClosedXML.Excel.CalcEngine;
-using DocumentFormat.OpenXml;
+using System.Linq;
 
 namespace ClosedXML.Excel
 {
-    using System.Linq;
-    using System.Data;
 
     public enum XLEventTracking { Enabled, Disabled }
     public enum XLCalculateMode
@@ -865,47 +865,34 @@
         public Boolean LockWindows { get; set; }
         public XLWorkbook SetLockWindows(Boolean value) { LockWindows = value; return this; }
         internal HexBinaryValue LockPassword { get; set; }
+        public Boolean IsPasswordProtected { get { return LockPassword != null; } }
         
         public void Protect(Boolean lockStructure, Boolean lockWindows, String workbookPassword)
         {
-            if (workbookPassword != null)
+            if (IsPasswordProtected && workbookPassword == null)
+                throw new InvalidOperationException("The workbook is password protected");
+
+            var hashPassword = workbookPassword.HashPassword();
+            if (IsPasswordProtected && LockPassword != hashPassword)
+                throw new ArgumentException("Invalid password");
+
+            if (IsPasswordProtected && (lockStructure || lockWindows))
+                throw new InvalidOperationException("The workbook is already protected");
+
+            if (IsPasswordProtected && hashPassword != null && !lockStructure && !lockWindows)
             {
-                var hashPassword = GetPasswordHash(workbookPassword);
-                if (LockPassword != null)
-                {
-                    if (LockPassword != hashPassword)
-                    {
-                        throw new ArgumentException("Invalid password");
-                    }
-                    else
-                    {
-                        if (lockStructure || lockWindows)
-                        {
-                            throw new InvalidOperationException("The workbook is already protected");
-                        }
-                        else
-                        {
-                            //Unprotect workbook using password.
-                            LockPassword = null;
-                        }
-                    }  
-                }
-                else
-                {
-                    if (lockStructure || lockWindows)
-                    {
-                        //Protect workbook using password.
-                        LockPassword = hashPassword;
-                    }
-                }
+                // Workbook currently protected, but we're unsetting the 2 flags
+                // Hence unprotect workbook using password.
+                LockPassword = null;
             }
-            else
+
+
+            if (!IsPasswordProtected && hashPassword != null && (lockStructure || lockWindows))
             {
-                if (LockPassword != null)
-                {
-                    throw new InvalidOperationException("The workbook is password protected");
-                }
+                //Protect workbook using password.
+                LockPassword = hashPassword;
             }
+
             LockStructure = lockStructure;
             LockWindows = lockWindows;
         }
@@ -939,21 +926,5 @@
         {
             Protect(false, false, workbookPassword);
         }
-
-        private String GetPasswordHash(String password)
-        {
-            Int32 pLength = password.Length;
-            Int32 hash = 0;
-            if (pLength == 0) return String.Empty;
-
-            for (Int32 i = pLength - 1; i >= 0; i--)
-            {
-                hash ^= password[i];
-                hash = hash >> 14 & 0x01 | hash << 1 & 0x7fff;
-            }
-            hash ^= 0x8000 | 'N' << 8 | 'K';
-            hash ^= pLength;
-            return hash.ToString("X");
-        }
     }
 }
\ No newline at end of file
diff --git a/ClosedXML/Extensions/StringExtensions.cs b/ClosedXML/Extensions/StringExtensions.cs
index a3b49ec..facf0a5 100644
--- a/ClosedXML/Extensions/StringExtensions.cs
+++ b/ClosedXML/Extensions/StringExtensions.cs
@@ -8,12 +8,31 @@
 {
     internal static class StringExtensions
     {
-        internal static string WrapSheetNameInQuotesIfRequired(this string sheetName)
+        internal static String WrapSheetNameInQuotesIfRequired(this String sheetName)
         {
             if (sheetName.Contains(' '))
                 return "'" + sheetName + "'";
             else
                 return sheetName;
         }
+
+        internal static String HashPassword(this String password)
+        {
+            if (password == null) return null;
+
+            Int32 pLength = password.Length;
+            Int32 hash = 0;
+            if (pLength == 0) return String.Empty;
+
+            for (Int32 i = pLength - 1; i >= 0; i--)
+            {
+                hash ^= password[i];
+                hash = hash >> 14 & 0x01 | hash << 1 & 0x7fff;
+            }
+            hash ^= 0x8000 | 'N' << 8 | 'K';
+            hash ^= pLength;
+            return hash.ToString("X");
+        }
+
     }
 }
diff --git a/ClosedXML_Tests/Excel/Misc/XLWorkbookTests.cs b/ClosedXML_Tests/Excel/Misc/XLWorkbookTests.cs
index 55afe19..5a1e4a7 100644
--- a/ClosedXML_Tests/Excel/Misc/XLWorkbookTests.cs
+++ b/ClosedXML_Tests/Excel/Misc/XLWorkbookTests.cs
@@ -255,7 +255,7 @@
             Assert.AreEqual("$A$1:$A$1", wsRanges.First().RangeAddress.ToStringFixed());
             Assert.AreEqual("$A$3:$A$3", wsRanges.Last().RangeAddress.ToStringFixed());
         }
-      
+
         [Test]
         public void WbProtect1()
         {
@@ -265,6 +265,7 @@
                 wb.Protect();
                 Assert.IsTrue(wb.LockStructure);
                 Assert.IsFalse(wb.LockWindows);
+                Assert.IsFalse(wb.IsPasswordProtected);
             }
         }
 
@@ -277,6 +278,7 @@
                 wb.Protect(true, false);
                 Assert.IsTrue(wb.LockStructure);
                 Assert.IsFalse(wb.LockWindows);
+                Assert.IsFalse(wb.IsPasswordProtected);
             }
         }
 
@@ -289,6 +291,7 @@
                 wb.Protect("Abc@123");
                 Assert.IsTrue(wb.LockStructure);
                 Assert.IsFalse(wb.LockWindows);
+                Assert.IsTrue(wb.IsPasswordProtected);
                 Assert.Throws(typeof(InvalidOperationException), delegate { wb.Protect(); });
                 Assert.Throws(typeof(InvalidOperationException), delegate { wb.Unprotect(); });
                 Assert.Throws(typeof(ArgumentException), delegate { wb.Unprotect("Cde@345"); });
@@ -304,9 +307,11 @@
                 wb.Protect();
                 Assert.IsTrue(wb.LockStructure);
                 Assert.IsFalse(wb.LockWindows);
+                Assert.IsFalse(wb.IsPasswordProtected);
                 wb.Protect("Abc@123");
                 Assert.IsTrue(wb.LockStructure);
                 Assert.IsFalse(wb.LockWindows);
+                Assert.IsTrue(wb.IsPasswordProtected);
             }
         }
 
@@ -319,10 +324,12 @@
                 wb.Protect(true, false, "Abc@123");
                 Assert.IsTrue(wb.LockStructure);
                 Assert.IsFalse(wb.LockWindows);
+                Assert.IsTrue(wb.IsPasswordProtected);
                 wb.Unprotect("Abc@123");
                 Assert.IsFalse(wb.LockStructure);
                 Assert.IsFalse(wb.LockWindows);
+                Assert.IsFalse(wb.IsPasswordProtected);
             }
         }
     }
-}
\ No newline at end of file
+}