diff --git a/demos/STM32/RT-STM32G474RE-NUCLEO64-SB_HOST_STATIC/Makefile b/demos/STM32/RT-STM32G474RE-NUCLEO64-SB_HOST_STATIC/Makefile
index 902e59d14..5ed72260f 100644
--- a/demos/STM32/RT-STM32G474RE-NUCLEO64-SB_HOST_STATIC/Makefile
+++ b/demos/STM32/RT-STM32G474RE-NUCLEO64-SB_HOST_STATIC/Makefile
@@ -5,7 +5,7 @@
 
 # Compiler options here.
 ifeq ($(USE_OPT),)
-  USE_OPT = -O2 -ggdb -fomit-frame-pointer -falign-functions=16
+  USE_OPT = -O0 -ggdb -fomit-frame-pointer -falign-functions=16
 endif
 
 # C specific options here (added to USE_OPT).
diff --git a/demos/various/SB-CLIENT-32k-08070000-4k-2001E000/main.c b/demos/various/SB-CLIENT-32k-08070000-4k-2001E000/main.c
index 66d2bb44b..ca5f6e216 100644
--- a/demos/various/SB-CLIENT-32k-08070000-4k-2001E000/main.c
+++ b/demos/various/SB-CLIENT-32k-08070000-4k-2001E000/main.c
@@ -18,6 +18,14 @@
 
 #include "sbuser.h"
 
+__attribute__((naked))
+void __crt0_vrq(int vrqn) {
+
+  (void)vrqn;
+
+  __sb_vrq_return();
+}
+
 /*
  * Application entry point.
  */
@@ -30,6 +38,9 @@ int main(void) {
   while (true) {
   }
 #endif
+  __sb_vrq_seten(2);
+  __sb_vrq_setwt(2);
+
   while (true) {
     msg_t msg = sbMsgWait();
     printf("#1 Hello World (%u)!!\r\n", (unsigned)msg);
diff --git a/os/sb/host/sbvrq.c b/os/sb/host/sbvrq.c
index 94ddadf5c..004de22ce 100644
--- a/os/sb/host/sbvrq.c
+++ b/os/sb/host/sbvrq.c
@@ -55,6 +55,9 @@ __STATIC_FORCEINLINE void vrq_makectx(sb_class_t *sbp,
   uint32_t irqn = __CLZ(active_mask);
   sbp->vrq_wtmask &= ~(1U << irqn);
 
+  /* Disabling VRQs globally during processing.*/
+  sbp->vrq_isr |= SB_VRQ_ISR_DISABLED;
+
   /* Building the return context.*/
   newctxp->r0     = irqn;
   newctxp->pc     = sbp->sbhp->hdr_vrq;