diff --git a/hw/adc/stm32f2xx_adc.c b/hw/adc/stm32f2xx_adc.c
index 4f9d485ecf..01a0b14e69 100644
--- a/hw/adc/stm32f2xx_adc.c
+++ b/hw/adc/stm32f2xx_adc.c
@@ -246,6 +246,8 @@ static const MemoryRegionOps stm32f2xx_adc_ops = {
     .read = stm32f2xx_adc_read,
     .write = stm32f2xx_adc_write,
     .endianness = DEVICE_NATIVE_ENDIAN,
+    .impl.min_access_size = 4,
+    .impl.max_access_size = 4,
 };
 
 static const VMStateDescription vmstate_stm32f2xx_adc = {
@@ -278,7 +280,7 @@ static void stm32f2xx_adc_init(Object *obj)
     sysbus_init_irq(SYS_BUS_DEVICE(obj), &s->irq);
 
     memory_region_init_io(&s->mmio, obj, &stm32f2xx_adc_ops, s,
-                          TYPE_STM32F2XX_ADC, 0xFF);
+                          TYPE_STM32F2XX_ADC, 0x100);
     sysbus_init_mmio(SYS_BUS_DEVICE(obj), &s->mmio);
 }