diff --git a/drivers/pinctrl/pinctrl-st.c b/drivers/pinctrl/pinctrl-st.c
index d3cea3437d7f..8ce88e591f47 100644
--- a/drivers/pinctrl/pinctrl-st.c
+++ b/drivers/pinctrl/pinctrl-st.c
@@ -987,6 +987,7 @@ static int st_pinconf_get(struct pinctrl_dev *pctldev,
 
 static void st_pinconf_dbg_show(struct pinctrl_dev *pctldev,
 				   struct seq_file *s, unsigned pin_id)
+	__must_hold(&pctldev->mutex)
 {
 	struct st_pio_control *pc;
 	unsigned long config;