diff --git a/hw/tpm/tpm_passthrough.c b/hw/tpm/tpm_passthrough.c
index e98efb709e..e88c0d20bc 100644
--- a/hw/tpm/tpm_passthrough.c
+++ b/hw/tpm/tpm_passthrough.c
@@ -86,7 +86,7 @@ static int tpm_passthrough_unix_write(int fd, const uint8_t *buf, uint32_t len)
     int ret, remain;
 
     remain = len;
-    while (len > 0) {
+    while (remain > 0) {
         ret = write(fd, buf, remain);
         if (ret < 0) {
             if (errno != EINTR && errno != EAGAIN) {