diff --git a/arch/arm/include/asm/bootm.h b/arch/arm/include/asm/bootm.h
index a2131ca..27f183b 100644
--- a/arch/arm/include/asm/bootm.h
+++ b/arch/arm/include/asm/bootm.h
@@ -41,9 +41,12 @@
 struct tag_serialnr;
 #ifdef CONFIG_SERIAL_TAG
  #define BOOTM_ENABLE_SERIAL_TAG	1
-void get_board_serial(struct tag_serialnr *serialnr);
 #else
  #define BOOTM_ENABLE_SERIAL_TAG	0
+#endif
+#if defined(CONFIG_SERIAL_TAG) || defined(CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG)
+void get_board_serial(struct tag_serialnr *serialnr);
+#else
 static inline void get_board_serial(struct tag_serialnr *serialnr)
 {
 }