diff --git a/configs/xtrs/src/xtr_serial.c b/configs/xtrs/src/xtr_serial.c
index 06a38058a29..dbe69df678f 100644
--- a/configs/xtrs/src/xtr_serial.c
+++ b/configs/xtrs/src/xtr_serial.c
@@ -58,12 +58,6 @@
 #include "os_internal.h"
 #include "up_internal.h"
 
-/* Defined in drivers/dev_lowconsole.c */
-
-#ifdef CONFIG_USE_LOWCONSOLE
-extern void lowconsole_init(void);
-#endif
-
 #if CONFIG_NFILE_DESCRIPTORS > 0
 #if defined(CONFIG_DEV_CONSOLE) && !defined(CONFIG_DEV_LOWCONSOLE)
 /****************************************************************************
diff --git a/configs/z80sim/src/z80_serial.c b/configs/z80sim/src/z80_serial.c
index b5a0c686320..42b0eecc14e 100644
--- a/configs/z80sim/src/z80_serial.c
+++ b/configs/z80sim/src/z80_serial.c
@@ -54,12 +54,6 @@
 #include "os_internal.h"
 #include "up_internal.h"
 
-/* Defined in drivers/dev_lowconsole.c */
-
-#ifdef CONFIG_USE_LOWCONSOLE
-extern void lowconsole_init(void);
-#endif
-
 #if CONFIG_NFILE_DESCRIPTORS > 0
 #if defined(CONFIG_DEV_CONSOLE) && !defined(CONFIG_DEV_LOWCONSOLE)
 /****************************************************************************