diff --git a/stm8s.h b/stm8s.h
index ebbcf1c..119bb2c 100644
--- a/stm8s.h
+++ b/stm8s.h
@@ -576,7 +576,7 @@ typedef struct {
 #define CLK_PCKENR1 (*(volatile uint8_t *)(CLK_BASE + 0x07))
 #define CLK_PCKENR1_I2C (1U << 0)
 #define CLK_PCKENR1_SPI (1U << 1)
-#define CLK_PCKENR1_UART1234 (3 << 2)
+#define CLK_PCKENR1_UART1234 (3U << 2)
 #define CLK_PCKENR1_TIM46 (1U << 4)
 #define CLK_PCKENR1_TIM25 (1U << 5)
 #define CLK_PCKENR1_TIM3 (1U << 6)