diff --git a/embed/trezorhal/common.c b/embed/trezorhal/common.c
index 1e219d929c..2983505b4d 100644
--- a/embed/trezorhal/common.c
+++ b/embed/trezorhal/common.c
@@ -43,6 +43,9 @@ void periph_init(void) {
     // Set the system clock to be HSE
     SystemClock_Config();
 
+    // Enable CSS (Clock Security System)
+    HAL_RCC_EnableCSS();
+
     // Enable GPIO clocks
     __HAL_RCC_GPIOA_CLK_ENABLE();
     __HAL_RCC_GPIOB_CLK_ENABLE();