diff --git a/master/cdev.c b/master/cdev.c
index 42e87cda117beb347ef337a621834bf64f9a5ecb..faad92ce3be171c64f598ff4bdf8556d42719a18 100644
--- a/master/cdev.c
+++ b/master/cdev.c
@@ -3449,7 +3449,7 @@ int ec_cdev_ioctl_slave_soe_write(
 
     data = kmalloc(ioctl.data_size, GFP_KERNEL);
     if (!data) {
-        EC_MASTER_ERR(master, "Failed to allocate %u bytes of IDN data.\n",
+        EC_MASTER_ERR(master, "Failed to allocate %zu bytes of IDN data.\n",
                 ioctl.data_size);
         return -ENOMEM;
     }
diff --git a/master/ioctl.h b/master/ioctl.h
index c926f562bb39f523ef0a8f8cd068a183f2a4c576..c2f695001f1f1a64900916be48122b9baf2b7c5b 100644
--- a/master/ioctl.h
+++ b/master/ioctl.h
@@ -56,7 +56,7 @@
  *
  * Increment this when changing the ioctl interface!
  */
-#define EC_IOCTL_VERSION_MAGIC 9
+#define EC_IOCTL_VERSION_MAGIC 10
 
 // Command-line tool
 #define EC_IOCTL_MODULE                EC_IOR(0x00, ec_ioctl_module_t)
@@ -421,7 +421,7 @@ typedef struct {
     uint8_t *data;
 
     // outputs
-    uint32_t data_size;
+    size_t data_size;
     uint16_t error_code;
 } ec_ioctl_slave_soe_read_t;
 
@@ -432,7 +432,7 @@ typedef struct {
     uint16_t slave_position;
     uint8_t drive_no;
     uint16_t idn;
-    uint32_t data_size;
+    size_t data_size;
     uint8_t *data;
 
     // outputs
@@ -530,7 +530,7 @@ typedef struct {
     uint8_t drive_no;
     uint16_t idn;
     ec_al_state_t state;
-    uint32_t size;
+    size_t size;
     uint8_t data[EC_MAX_IDN_DATA_SIZE];
 } ec_ioctl_config_idn_t;