diff --git a/hw/tpm/tpm_passthrough.c b/hw/tpm/tpm_passthrough.c
index 788be3847d..73554aa792 100644
--- a/hw/tpm/tpm_passthrough.c
+++ b/hw/tpm/tpm_passthrough.c
@@ -89,6 +89,7 @@ static int tpm_passthrough_unix_tx_bufs(TPMPassthruState *tpm_pt,
     bool is_selftest;
     const struct tpm_resp_hdr *hdr;
 
+    /* FIXME: protect shared variables or use other sync mechanism */
     tpm_pt->tpm_op_canceled = false;
     tpm_pt->tpm_executing = true;
     *selftest_done = false;
@@ -178,12 +179,11 @@ static void tpm_passthrough_cancel_cmd(TPMBackend *tb)
      */
     if (tpm_pt->tpm_executing) {
         if (tpm_pt->cancel_fd >= 0) {
+            tpm_pt->tpm_op_canceled = true;
             n = write(tpm_pt->cancel_fd, "-", 1);
             if (n != 1) {
                 error_report("Canceling TPM command failed: %s",
                              strerror(errno));
-            } else {
-                tpm_pt->tpm_op_canceled = true;
             }
         } else {
             error_report("Cannot cancel TPM command due to missing "