diff --git a/os/hal/osal/os-less/ARMCMx/osal.h b/os/hal/osal/os-less/ARMCMx/osal.h
index 248af8831..14ba6b115 100644
--- a/os/hal/osal/os-less/ARMCMx/osal.h
+++ b/os/hal/osal/os-less/ARMCMx/osal.h
@@ -598,6 +598,11 @@ static inline void osalSysLockFromISR(void) {
  */
 static inline void osalSysUnlockFromISR(void) {
 
+#if CORTEX_MODEL == 0
+  __enable_irq();
+#else
+  __set_BASEPRI(0);
+#endif
 }
 
 /**
diff --git a/readme.txt b/readme.txt
index 95c594290..aa3ed17c4 100644
--- a/readme.txt
+++ b/readme.txt
@@ -160,6 +160,8 @@
 - EX:  Updated LIS302DL to 1.1.0 (backported to 18.2.1).
 - EX:  Updated LPS25H to 1.1.0 (backported to 18.2.1).
 - EX:  Updated LSM303DLHC to 1.1.0 (backported to 18.2.1).
+- HAL: Fixed OS-Less Cortex-M HAL functionality broken (bug #987)
+       (backported to 18.2.2).
 - HAL: Fixed broken functionality of MFS module (bug #986).
 - NIL: Fixed scheduler misbehaving in rare cases (bug #983)
        (backported to 18.2.2 and 17.6.5).