diff --git a/AutoTx/AutoTx.cs b/AutoTx/AutoTx.cs
index 5dd7a992a02df9cc1fbfbd7fa123c1c9b205656d..f4dfd510f78aafde5a07c8af2e5b0b7e9f11dc51 100644
--- a/AutoTx/AutoTx.cs
+++ b/AutoTx/AutoTx.cs
@@ -29,6 +29,9 @@ namespace AutoTx
 
         private int _txProgress;
 
+        private const int MegaBytes = 1024 * 1024;
+        private const int GigaBytes = 1024 * 1024 * 1024;
+
         private DateTime _lastUserDirCheck = DateTime.Now;
 
         // the transfer state:
diff --git a/AutoTx/SystemChecks.cs b/AutoTx/SystemChecks.cs
index 67a04893c2b6a4540b92795f6dd130cfc20ee808..4e7cad20b42b97c5c7fcfec928f02a50224e0b17 100644
--- a/AutoTx/SystemChecks.cs
+++ b/AutoTx/SystemChecks.cs
@@ -61,7 +61,7 @@ namespace AutoTx
         private long GetFreeDriveSpace(string drive) {
             try {
                 var dInfo = new DriveInfo(drive);
-                return dInfo.TotalFreeSpace / 1048576; // convert bytes to MB
+                return dInfo.TotalFreeSpace / MegaBytes;
             }
             catch (Exception ex) {
                 writeLog("Error in GetFreeDriveSpace(" + drive + "): " + ex.Message);