diff --git a/include/libopencm3/stm32/common/flash_common_f234.h b/include/libopencm3/stm32/common/flash_common_f234.h
index a012cf6e..19247c4e 100644
--- a/include/libopencm3/stm32/common/flash_common_f234.h
+++ b/include/libopencm3/stm32/common/flash_common_f234.h
@@ -50,6 +50,7 @@
 
 /* --- FLASH_ACR values ---------------------------------------------------- */
 
+#define FLASH_ACR_LATENCY_MASK		0x07
 #define FLASH_ACR_LATENCY_0WS		0x00
 #define FLASH_ACR_LATENCY_1WS		0x01
 #define FLASH_ACR_LATENCY_2WS		0x02
diff --git a/lib/stm32/common/flash_common_f234.c b/lib/stm32/common/flash_common_f234.c
index 33ca226b..1977fbbe 100644
--- a/lib/stm32/common/flash_common_f234.c
+++ b/lib/stm32/common/flash_common_f234.c
@@ -41,7 +41,7 @@ void flash_set_ws(uint32_t ws)
 	uint32_t reg32;
 
 	reg32 = FLASH_ACR;
-	reg32 &= ~((1 << 0) | (1 << 1) | (1 << 2));
+	reg32 &= ~(FLASH_ACR_LATENCY_MASK);
 	reg32 |= ws;
 	FLASH_ACR = reg32;
 }