diff --git a/hw/acpi/erst.c b/hw/acpi/erst.c
index df856b2669..aefcc03ad6 100644
--- a/hw/acpi/erst.c
+++ b/hw/acpi/erst.c
@@ -635,7 +635,7 @@ static unsigned read_erst_record(ERSTDeviceState *s)
         if (record_length < UEFI_CPER_RECORD_MIN_SIZE) {
             rc = STATUS_FAILED;
         }
-        if ((s->record_offset + record_length) > exchange_length) {
+        if (record_length > exchange_length - s->record_offset) {
             rc = STATUS_FAILED;
         }
         /* If all is ok, copy the record to the exchange buffer */
@@ -684,7 +684,7 @@ static unsigned write_erst_record(ERSTDeviceState *s)
     if (record_length < UEFI_CPER_RECORD_MIN_SIZE) {
         return STATUS_FAILED;
     }
-    if ((s->record_offset + record_length) > exchange_length) {
+    if (record_length > exchange_length - s->record_offset) {
         return STATUS_FAILED;
     }
 
@@ -716,7 +716,7 @@ static unsigned write_erst_record(ERSTDeviceState *s)
     if (nvram) {
         /* Write the record into the slot */
         memcpy(nvram, exchange, record_length);
-        memset(nvram + record_length, exchange_length - record_length, 0xFF);
+        memset(nvram + record_length, 0xFF, exchange_length - record_length);
         /* If a new record, increment the record_count */
         if (!record_found) {
             uint32_t record_count;