diff --git a/include/ecrt.h b/include/ecrt.h
index cd4e1a3f..00de58b7 100644
--- a/include/ecrt.h
+++ b/include/ecrt.h
@@ -815,7 +815,7 @@ int ecrt_master_sdo_download(
         uint16_t slave_position, /**< Slave position. */
         uint16_t index, /**< Index of the SDO. */
         uint8_t subindex, /**< Subindex of the SDO. */
-        uint8_t *data, /**< Data buffer to download. */
+        const uint8_t *data, /**< Data buffer to download. */
         size_t data_size, /**< Size of the data buffer. */
         uint32_t *abort_code /**< Abort code of the SDO download. */
         );
@@ -834,7 +834,7 @@ int ecrt_master_sdo_download_complete(
         ec_master_t *master, /**< EtherCAT master. */
         uint16_t slave_position, /**< Slave position. */
         uint16_t index, /**< Index of the SDO. */
-        uint8_t *data, /**< Data buffer to download. */
+        const uint8_t *data, /**< Data buffer to download. */
         size_t data_size, /**< Size of the data buffer. */
         uint32_t *abort_code /**< Abort code of the SDO download. */
         );
diff --git a/lib/master.c b/lib/master.c
index e0cf558f..8650a3a4 100644
--- a/lib/master.c
+++ b/lib/master.c
@@ -390,7 +390,7 @@ int ecrt_master_get_pdo_entry(ec_master_t *master, uint16_t slave_position,
 /****************************************************************************/
 
 int ecrt_master_sdo_download(ec_master_t *master, uint16_t slave_position,
-        uint16_t index, uint8_t subindex, uint8_t *data,
+        uint16_t index, uint8_t subindex, const uint8_t *data,
         size_t data_size, uint32_t *abort_code)
 {
     ec_ioctl_slave_sdo_download_t download;
@@ -419,7 +419,7 @@ int ecrt_master_sdo_download(ec_master_t *master, uint16_t slave_position,
 /****************************************************************************/
 
 int ecrt_master_sdo_download_complete(ec_master_t *master,
-        uint16_t slave_position, uint16_t index, uint8_t *data,
+        uint16_t slave_position, uint16_t index, const uint8_t *data,
         size_t data_size, uint32_t *abort_code)
 {
     ec_ioctl_slave_sdo_download_t download;
diff --git a/master/ioctl.c b/master/ioctl.c
index 087378dd..a55a5c1a 100755
--- a/master/ioctl.c
+++ b/master/ioctl.c
@@ -864,7 +864,7 @@ static ATTRIBUTES int ec_ioctl_slave_sdo_download(
         return -ENOMEM;
     }
 
-    if (copy_from_user(sdo_data, (void __user *) data.data, data.data_size)) {
+    if (copy_from_user(sdo_data, (const void __user *) data.data, data.data_size)) {
         kfree(sdo_data);
         return -EFAULT;
     }
diff --git a/master/ioctl.h b/master/ioctl.h
index 8fe55e62..b5296ea1 100644
--- a/master/ioctl.h
+++ b/master/ioctl.h
@@ -400,7 +400,7 @@ typedef struct {
     uint8_t sdo_entry_subindex;
     uint8_t complete_access;
     size_t data_size;
-    uint8_t *data;
+    const uint8_t *data;
 
     // outputs
     uint32_t abort_code;
diff --git a/master/master.c b/master/master.c
index 943be201..ebaa137d 100644
--- a/master/master.c
+++ b/master/master.c
@@ -2849,7 +2849,7 @@ uint32_t ecrt_master_sync_monitor_process(ec_master_t *master)
 /*****************************************************************************/
 
 int ecrt_master_sdo_download(ec_master_t *master, uint16_t slave_position,
-        uint16_t index, uint8_t subindex, uint8_t *data,
+        uint16_t index, uint8_t subindex, const uint8_t *data,
         size_t data_size, uint32_t *abort_code)
 {
     ec_sdo_request_t request;
@@ -2933,7 +2933,7 @@ int ecrt_master_sdo_download(ec_master_t *master, uint16_t slave_position,
 /*****************************************************************************/
 
 int ecrt_master_sdo_download_complete(ec_master_t *master,
-        uint16_t slave_position, uint16_t index, uint8_t *data,
+        uint16_t slave_position, uint16_t index, const uint8_t *data,
         size_t data_size, uint32_t *abort_code)
 {
     ec_sdo_request_t request;
diff --git a/tool/CommandDownload.cpp b/tool/CommandDownload.cpp
index 0ee59d32..b69ef094 100644
--- a/tool/CommandDownload.cpp
+++ b/tool/CommandDownload.cpp
@@ -173,16 +173,17 @@ void CommandDownload::execute(const StringVector &args)
             throwCommandException(err);
         }
         data.data_size = contents.size();
-        data.data = new uint8_t[data.data_size + 1];
+        uint8_t *sdo_data = new uint8_t[data.data_size + 1];
+        data.data = sdo_data;
 
         try {
             data.data_size = interpretAsType(
-                    dataType, contents, data.data, data.data_size);
+                    dataType, contents, sdo_data, data.data_size);
         } catch (SizeException &e) {
-            delete [] data.data;
+            delete [] sdo_data;
             throwCommandException(e.what());
         } catch (ios::failure &e) {
-            delete [] data.data;
+            delete [] sdo_data;
             err << "Invalid value argument '" << args[2]
                 << "' for type '" << dataType->name << "'!";
             throwInvalidUsageException(err);
@@ -195,35 +196,23 @@ void CommandDownload::execute(const StringVector &args)
             data.data_size = DefaultBufferSize;
         }
 
-        data.data = new uint8_t[data.data_size + 1];
+        uint8_t *sdo_data = new uint8_t[data.data_size + 1];
+        data.data = sdo_data;
 
         try {
             data.data_size = interpretAsType(
-                    dataType, args[valueIndex], data.data, data.data_size);
+                    dataType, args[valueIndex], sdo_data, data.data_size);
         } catch (SizeException &e) {
-            delete [] data.data;
+            delete [] sdo_data;
             throwCommandException(e.what());
         } catch (ios::failure &e) {
-            delete [] data.data;
+            delete [] sdo_data;
             err << "Invalid value argument '" << args[2]
                 << "' for type '" << dataType->name << "'!";
             throwInvalidUsageException(err);
         }
     }
 
-    try {
-        data.data_size = interpretAsType(
-                dataType, args[valueIndex], data.data, data.data_size);
-    } catch (SizeException &e) {
-        delete [] data.data;
-        throwCommandException(e.what());
-    } catch (ios::failure &e) {
-        delete [] data.data;
-        err << "Invalid value argument '" << args[2]
-            << "' for type '" << dataType->name << "'!";
-        throwInvalidUsageException(err);
-    }
-
     try {
         m.sdoDownload(&data);
     } catch (MasterDeviceSdoAbortException &e) {