diff --git a/Steamless.API/PE32/Pe32Helpers.cs b/Steamless.API/PE32/Pe32Helpers.cs
index 8d33b5a..4874bac 100644
--- a/Steamless.API/PE32/Pe32Helpers.cs
+++ b/Steamless.API/PE32/Pe32Helpers.cs
@@ -90,49 +90,6 @@ namespace Steamless.API.PE32
             return GetStructure<NativeApi32.ImageSectionHeader32>(rawData, dataOffset + (index * sectionSize));
         }
 
-        /// <summary>
-        /// Calculates the PE checksum of the opened file. (OptionalHeader.Checksum should be 0 before calling this!)
-        /// </summary>
-        /// <param name="fStream"></param>
-        /// <returns></returns>
-        private static byte[] CalculateChecksum(FileStream fStream)
-        {
-            fStream.Position = 0;
-
-            var dataSize = fStream.Length;
-            var totalWords = dataSize / 2;
-            var sumTotal = 0;
-
-            // Process the file data in uint16_t chunks..
-            while (totalWords > 0)
-            {
-                var sumChunk = 0;
-                var chunkWords = totalWords;
-
-                // Prepare next chunk size..
-                if (chunkWords > UInt16.MaxValue)
-                    chunkWords = UInt16.MaxValue;
-
-                totalWords -= chunkWords;
-
-                do
-                {
-                    var data = new byte[2];
-                    fStream.Read(data, 0, 2);
-                    sumChunk += BitConverter.ToUInt16(data, 0);
-                } while (--chunkWords != 0);
-
-                sumTotal += (sumChunk >> 16) + (sumChunk & 0xFFFF);
-            }
-
-            if ((dataSize % 2) != 0)
-                sumTotal += fStream.ReadByte();
-
-            var checksum = (uint)(((sumTotal >> 16) + (sumTotal & 0xFFFF)) + dataSize);
-
-            return BitConverter.GetBytes(checksum);
-        }
-
         /// <summary>
         /// Updates the given files PE checksum value. (Path is assumed to be a 32bit PE file.)
         /// </summary>
@@ -140,6 +97,11 @@ namespace Steamless.API.PE32
         /// <returns></returns>
         public static bool UpdateFileChecksum(string path)
         {
+            // Obtain the proper checksum for the file..
+            var ret = NativeApi32.MapFileAndCheckSum(path, out uint HeaderSum, out uint Checksum);
+            if (ret != 0)
+                return false;
+
             FileStream fStream = null;
             var data = new byte[4];
 
@@ -158,17 +120,10 @@ namespace Steamless.API.PE32
                 offset += 4 + (uint)Marshal.SizeOf(typeof(NativeApi32.ImageFileHeader32)) + (uint)Marshal.OffsetOf(typeof(NativeApi32.ImageOptionalHeader32), "CheckSum").ToInt32();
                 fStream.Position = offset;
 
-                // Ensure the checksum is 0 to start..
-                data = new byte[4] { 0, 0, 0, 0 };
+                // Overwrite the file checksum..
+                data = BitConverter.GetBytes(Checksum);
                 fStream.Write(data, 0, 4);
 
-                // Calculate the new checksum..
-                var checksum = CalculateChecksum(fStream);
-
-                // Update the checksum value..
-                fStream.Position = offset;
-                fStream.Write(checksum, 0, 4);
-
                 return true;
             }
             catch
diff --git a/Steamless.API/PE64/Pe64Helpers.cs b/Steamless.API/PE64/Pe64Helpers.cs
index d3e8289..4ac472f 100644
--- a/Steamless.API/PE64/Pe64Helpers.cs
+++ b/Steamless.API/PE64/Pe64Helpers.cs
@@ -90,49 +90,6 @@ namespace Steamless.API.PE64
             return GetStructure<NativeApi64.ImageSectionHeader64>(rawData, (int)dataOffset + (index * sectionSize));
         }
 
-        /// <summary>
-        /// Calculates the PE checksum of the opened file. (OptionalHeader.Checksum should be 0 before calling this!)
-        /// </summary>
-        /// <param name="fStream"></param>
-        /// <returns></returns>
-        private static byte[] CalculateChecksum(FileStream fStream)
-        {
-            fStream.Position = 0;
-
-            var dataSize = fStream.Length;
-            var totalWords = dataSize / 2;
-            var sumTotal = 0;
-
-            // Process the file data in uint16_t chunks..
-            while (totalWords > 0)
-            {
-                var sumChunk = 0;
-                var chunkWords = totalWords;
-
-                // Prepare next chunk size..
-                if (chunkWords > UInt16.MaxValue)
-                    chunkWords = UInt16.MaxValue;
-
-                totalWords -= chunkWords;
-
-                do
-                {
-                    var data = new byte[2];
-                    fStream.Read(data, 0, 2);
-                    sumChunk += BitConverter.ToUInt16(data, 0);
-                } while (--chunkWords != 0);
-
-                sumTotal += (sumChunk >> 16) + (sumChunk & 0xFFFF);
-            }
-
-            if ((dataSize % 2) != 0)
-                sumTotal += fStream.ReadByte();
-
-            var checksum = (uint)(((sumTotal >> 16) + (sumTotal & 0xFFFF)) + dataSize);
-
-            return BitConverter.GetBytes(checksum);
-        }
-
         /// <summary>
         /// Updates the given files PE checksum value. (Path is assumed to be a 32bit PE file.)
         /// </summary>
@@ -140,6 +97,11 @@ namespace Steamless.API.PE64
         /// <returns></returns>
         public static bool UpdateFileChecksum(string path)
         {
+            // Obtain the proper checksum for the file..
+            var ret = NativeApi64.MapFileAndCheckSum(path, out uint HeaderSum, out uint Checksum);
+            if (ret != 0)
+                return false;
+
             FileStream fStream = null;
             var data = new byte[4];
 
@@ -158,17 +120,10 @@ namespace Steamless.API.PE64
                 offset += 4 + (uint)Marshal.SizeOf(typeof(NativeApi64.ImageFileHeader64)) + (uint)Marshal.OffsetOf(typeof(NativeApi64.ImageOptionalHeader64), "CheckSum").ToInt32();
                 fStream.Position = offset;
 
-                // Ensure the checksum is 0 to start..
-                data = new byte[4] { 0, 0, 0, 0 };
+                // Overwrite the file checksum..
+                data = BitConverter.GetBytes(Checksum);
                 fStream.Write(data, 0, 4);
 
-                // Calculate the new checksum..
-                var checksum = CalculateChecksum(fStream);
-
-                // Update the checksum value..
-                fStream.Position = offset;
-                fStream.Write(checksum, 0, 4);
-
                 return true;
             }
             catch
diff --git a/Steamless.API/Properties/AssemblyInfo.cs b/Steamless.API/Properties/AssemblyInfo.cs
index 5bc7c92..1e09250 100644
--- a/Steamless.API/Properties/AssemblyInfo.cs
+++ b/Steamless.API/Properties/AssemblyInfo.cs
@@ -36,5 +36,5 @@ using System.Runtime.InteropServices;
 [assembly: AssemblyCulture("")]
 [assembly: ComVisible(false)]
 [assembly: Guid("56c95629-3b34-47fe-b988-04274409294f")]
-[assembly: AssemblyVersion("1.0.0.5")]
-[assembly: AssemblyFileVersion("1.0.0.5")]
\ No newline at end of file
+[assembly: AssemblyVersion("1.0.0.6")]
+[assembly: AssemblyFileVersion("1.0.0.6")]
\ No newline at end of file