diff --git a/tmk_core/protocol/chibios/usb_endpoints.h b/tmk_core/protocol/chibios/usb_endpoints.h
index a4e5ed88fce..9fad83726e9 100644
--- a/tmk_core/protocol/chibios/usb_endpoints.h
+++ b/tmk_core/protocol/chibios/usb_endpoints.h
@@ -121,7 +121,7 @@ typedef enum {
 
 #define IS_VALID_USB_ENDPOINT_IN_LUT(i) ((i) >= 0 && (i) < USB_ENDPOINT_IN_COUNT)
 
-usb_endpoint_in_lut_t usb_endpoint_interface_lut[TOTAL_INTERFACES];
+extern usb_endpoint_in_lut_t usb_endpoint_interface_lut[TOTAL_INTERFACES];
 
 typedef enum {
 #if defined(RAW_ENABLE)