diff --git a/testhal/STM32/IRQ_STORM/main.c b/testhal/STM32/IRQ_STORM/main.c
index b20369b47..71ff38440 100644
--- a/testhal/STM32/IRQ_STORM/main.c
+++ b/testhal/STM32/IRQ_STORM/main.c
@@ -39,7 +39,7 @@
 #endif
 
 #ifndef MAILBOX_SIZE
-#define MAILBOX_SIZE    2
+#define MAILBOX_SIZE    4
 #endif
 
 /*===========================================================================*/