diff --git a/src/util/externalcommand.h b/src/util/externalcommand.h
--- a/src/util/externalcommand.h
+++ b/src/util/externalcommand.h
@@ -68,8 +68,8 @@
     ~ExternalCommand();
 
 public:
-    bool copyBlocks(CopySource& source, CopyTarget& target);
-    bool writeData(Report& report, const QByteArray& buffer, const QString& deviceNode, const quint64 firstByte); // same as copyBlocks but from QByteArray
+    bool copyBlocks(const CopySource& source, CopyTarget& target);
+    bool writeData(Report& commandReport, const QByteArray& buffer, const QString& deviceNode, const quint64 firstByte); // same as copyBlocks but from QByteArray
 
     /**< @param cmd the command to run */
     void setCommand(const QString& cmd);
diff --git a/src/util/externalcommand.cpp b/src/util/externalcommand.cpp
--- a/src/util/externalcommand.cpp
+++ b/src/util/externalcommand.cpp
@@ -183,7 +183,7 @@
     return rval;
 }
 
-bool ExternalCommand::copyBlocks(CopySource& source, CopyTarget& target)
+bool ExternalCommand::copyBlocks(const CopySource& source, CopyTarget& target)
 {
     bool rval = true;
     const qint64 blockSize = 10 * 1024 * 1024; // number of bytes per block to copy