diff --git a/lib/device/dev-io.c b/lib/device/dev-io.c
index fde59df9e..7dbc462ab 100644
--- a/lib/device/dev-io.c
+++ b/lib/device/dev-io.c
@@ -212,7 +212,7 @@ static int _aligned_io(struct device_area *where, void *buffer,
  * Public functions
  *---------------------------------------------------------------*/
 
-int dev_get_size(struct device *dev, uint64_t *size)
+int dev_get_size(const struct device *dev, uint64_t *size)
 {
 	int fd;
 	const char *name = dev_name(dev);
diff --git a/lib/device/device.h b/lib/device/device.h
index cc9dff4c7..2c93ca507 100644
--- a/lib/device/device.h
+++ b/lib/device/device.h
@@ -55,7 +55,7 @@ struct device_area {
 /*
  * All io should use these routines.
  */
-int dev_get_size(struct device *dev, uint64_t *size);
+int dev_get_size(const struct device *dev, uint64_t *size);
 int dev_get_sectsize(struct device *dev, uint32_t *size);
 
 /* Use quiet version if device number could change e.g. when opening LV */