diff --git a/os/ex/devices/ADI/adxl355.c b/os/ex/devices/ADI/adxl355.c
index de9be045e..cc0d52b51 100644
--- a/os/ex/devices/ADI/adxl355.c
+++ b/os/ex/devices/ADI/adxl355.c
@@ -178,7 +178,7 @@ static msg_t acc_read_cooked(void *ip, float axes[]) {
   ADXL355Driver* devp;
   uint32_t i;
   int32_t raw[ADXL355_ACC_NUMBER_OF_AXES];
-  msg_t msg;
+  msg_t msg = MSG_OK;
 
   osalDbgCheck((ip != NULL) && (axes != NULL));
 
@@ -341,7 +341,7 @@ static msg_t acc_reset_sensivity(void *ip) {
 static msg_t acc_set_full_scale(ADXL355Driver *devp, adxl355_acc_fs_t fs) {
   float newfs, scale;
   uint8_t i, reg_val;
-  msg_t msg;
+  msg_t msg = MSG_OK;
 
   osalDbgCheck(devp != NULL);
 
diff --git a/testex/STM32/STM32F4xx/SPI-ADXL355/Makefile b/testex/STM32/STM32F4xx/SPI-ADXL355/Makefile
index 52806030b..c6c064253 100644
--- a/testex/STM32/STM32F4xx/SPI-ADXL355/Makefile
+++ b/testex/STM32/STM32F4xx/SPI-ADXL355/Makefile
@@ -5,7 +5,7 @@
 
 # Compiler options here.
 ifeq ($(USE_OPT),)
-  USE_OPT = -O0 -ggdb -fomit-frame-pointer -falign-functions=16
+  USE_OPT = -O2 -ggdb -fomit-frame-pointer -falign-functions=16
 endif
 
 # C specific options here (added to USE_OPT).