diff --git a/rtos/rtx5/mbed_rtx_conf.h b/rtos/rtx5/mbed_rtx_conf.h
index 7558cddf0b..f547700720 100644
--- a/rtos/rtx5/mbed_rtx_conf.h
+++ b/rtos/rtx5/mbed_rtx_conf.h
@@ -38,7 +38,7 @@
 
 #if defined(__CC_ARM)
 #define OS_MUTEX_OBJ_MEM            1
-#define OS_MUTEX_NUM                7
+#define OS_MUTEX_NUM                8
 #endif
 
 #if !defined(OS_STACK_WATERMARK) && (defined(MBED_STACK_STATS_ENABLED) && MBED_STACK_STATS_ENABLED)