diff --git a/hwaccess.c b/hwaccess.c
index 48ccb34..3a9ca57 100644
--- a/hwaccess.c
+++ b/hwaccess.c
@@ -247,7 +247,7 @@
 #define register_undo_mmio_write(a, c)					\
 {									\
 	struct undo_mmio_write_data *undo_mmio_write_data;		\
-	undo_mmio_write_data = malloc(sizeof(struct undo_mmio_write_data)); \
+	undo_mmio_write_data = malloc(sizeof(*undo_mmio_write_data));	\
 	if (!undo_mmio_write_data) {					\
 		msg_gerr("Out of memory!\n");				\
 		exit(1);						\