diff --git a/os/hal/src/hal_sio.c b/os/hal/src/hal_sio.c
index 4e8ab3e21..5c465720c 100644
--- a/os/hal/src/hal_sio.c
+++ b/os/hal/src/hal_sio.c
@@ -465,6 +465,9 @@ msg_t sioSynchronizeRX(SIODriver *siop, sysinterval_t timeout) {
   while (sio_lld_is_rx_empty(siop)) {
   /*lint -restore*/
     msg = osalThreadSuspendTimeoutS(&siop->sync_rx, timeout);
+    if (msg != MSG_OK) {
+      break;
+    }
   }
 
   osalSysUnlock();
@@ -502,6 +505,9 @@ msg_t sioSynchronizeTX(SIODriver *siop, sysinterval_t timeout) {
   while (sio_lld_is_tx_full(siop)) {
   /*lint -restore*/
     msg = osalThreadSuspendTimeoutS(&siop->sync_tx, timeout);
+    if (msg != MSG_OK) {
+      break;
+    }
   }
 
   osalSysUnlock();
diff --git a/readme.txt b/readme.txt
index d621dad39..41c78b9f6 100644
--- a/readme.txt
+++ b/readme.txt
@@ -110,6 +110,8 @@
        ARMv7-M and ARMv8-M-ML.
 - NEW: On STM32WBxx added a check on STM32_LSI_ENABLE required by IWDG.
 - NEW: Added SPIv2 support also to STM32WB and STM32WL.
+- FIX: Fixed missing exit condition in sioSynchronizeRX() and
+       sioSynchronizeTX() (bug #1211)(backported to 21.11.2).
 - FIX: Fixed missing check in chobjcaches.h (bug #1210)
        (backported to 20.3.5)(backported to 21.11.2).
 - FIX: Fixed misspelled chTraceSuspendI() function name (bug #1209)