diff --git a/include/linux/usb/of.h b/include/linux/usb/of.h
index 3805757dcdc2..974bce93aa28 100644
--- a/include/linux/usb/of.h
+++ b/include/linux/usb/of.h
@@ -17,7 +17,8 @@ bool of_usb_host_tpl_support(struct device_node *np);
 int of_usb_update_otg_caps(struct device_node *np,
 			struct usb_otg_caps *otg_caps);
 #else
-enum usb_dr_mode of_usb_get_dr_mode_by_phy(struct device_node *phy_np)
+static inline enum usb_dr_mode
+of_usb_get_dr_mode_by_phy(struct device_node *phy_np)
 {
 	return USB_DR_MODE_UNKNOWN;
 }