diff --git a/drivers/st/clk/stm32mp1_clk.c b/drivers/st/clk/stm32mp1_clk.c
index 6ada96a..dbe2b83 100644
--- a/drivers/st/clk/stm32mp1_clk.c
+++ b/drivers/st/clk/stm32mp1_clk.c
@@ -1652,7 +1652,7 @@
 	    (clksrc != (uint32_t)CLK_RTC_DISABLED)) {
 		mmio_clrsetbits_32(address,
 				   RCC_BDCR_RTCSRC_MASK,
-				   clksrc << RCC_BDCR_RTCSRC_SHIFT);
+				   (clksrc & RCC_SELR_SRC_MASK) << RCC_BDCR_RTCSRC_SHIFT);
 
 		mmio_setbits_32(address, RCC_BDCR_RTCCKEN);
 	}