diff --git a/hal/stm32u5.h b/hal/stm32u5.h
index 8578938bf1..cb1fd7feec 100644
--- a/hal/stm32u5.h
+++ b/hal/stm32u5.h
@@ -210,7 +210,7 @@
 #define FLASH_CR_PER                        (1 << 1)
 #define FLASH_CR_MER1                       (1 << 2)
 #define FLASH_CR_PNB_SHIFT                  3
-#define FLASH_CR_PNB_MASK                   0x7F
+#define FLASH_CR_PNB_MASK                   0xFF	/* RM0456 - Table 79 */
 #define FLASH_CR_BKER                       (1 << 11)
 #define FLASH_CR_MER2                       (1 << 15)
 #define FLASH_CR_STRT                       (1 << 16)