diff --git a/src/soc/mediatek/common/rtc_mt6359p.c b/src/soc/mediatek/common/rtc_mt6359p.c
index a930aacb87..6e8a3a0931 100644
--- a/src/soc/mediatek/common/rtc_mt6359p.c
+++ b/src/soc/mediatek/common/rtc_mt6359p.c
@@ -283,7 +283,7 @@ err:
 }
 
 /* enable rtc bbpu */
-void rtc_bbpu_power_on(void)
+static void rtc_bbpu_power_on(void)
 {
 	u16 bbpu;
 	int ret;
diff --git a/src/soc/mediatek/mt8183/include/soc/rtc.h b/src/soc/mediatek/mt8183/include/soc/rtc.h
index eb166a32a2..93fd29bf68 100644
--- a/src/soc/mediatek/mt8183/include/soc/rtc.h
+++ b/src/soc/mediatek/mt8183/include/soc/rtc.h
@@ -80,7 +80,6 @@ enum {
 
 
 /* external API */
-void rtc_bbpu_power_on(void);
 int rtc_init(int recover);
 bool rtc_gpio_init(void);
 void rtc_boot(void);
diff --git a/src/soc/mediatek/mt8183/rtc.c b/src/soc/mediatek/mt8183/rtc.c
index 40830b033f..23a3ea3d5c 100644
--- a/src/soc/mediatek/mt8183/rtc.c
+++ b/src/soc/mediatek/mt8183/rtc.c
@@ -263,7 +263,7 @@ err:
 }
 
 /* enable rtc bbpu */
-void rtc_bbpu_power_on(void)
+static void rtc_bbpu_power_on(void)
 {
 	u16 bbpu;
 	int ret;
diff --git a/src/soc/mediatek/mt8186/include/soc/rtc.h b/src/soc/mediatek/mt8186/include/soc/rtc.h
index 914da6ac83..fcd2f69b34 100644
--- a/src/soc/mediatek/mt8186/include/soc/rtc.h
+++ b/src/soc/mediatek/mt8186/include/soc/rtc.h
@@ -85,7 +85,6 @@ enum {
 
 
 /* external API */
-void rtc_bbpu_power_on(void);
 int rtc_init(int recover);
 bool rtc_gpio_init(void);
 void rtc_boot(void);
diff --git a/src/soc/mediatek/mt8186/rtc.c b/src/soc/mediatek/mt8186/rtc.c
index 7bf5bc8c0f..d3b148f824 100644
--- a/src/soc/mediatek/mt8186/rtc.c
+++ b/src/soc/mediatek/mt8186/rtc.c
@@ -301,7 +301,7 @@ err:
 }
 
 /* Enable RTC bbpu */
-void rtc_bbpu_power_on(void)
+static void rtc_bbpu_power_on(void)
 {
 	u16 bbpu;
 	int ret;
diff --git a/src/soc/mediatek/mt8188/include/soc/rtc.h b/src/soc/mediatek/mt8188/include/soc/rtc.h
index b2eb3f1f39..67a67017d9 100644
--- a/src/soc/mediatek/mt8188/include/soc/rtc.h
+++ b/src/soc/mediatek/mt8188/include/soc/rtc.h
@@ -84,7 +84,6 @@ enum {
 
 void rtc_read(u16 addr, u16 *rdata);
 void rtc_write(u16 addr, u16 wdata);
-void rtc_bbpu_power_on(void);
 int rtc_init(int recover);
 bool rtc_gpio_init(void);
 void rtc_boot(void);
diff --git a/src/soc/mediatek/mt8192/include/soc/rtc.h b/src/soc/mediatek/mt8192/include/soc/rtc.h
index f8543ab45d..10a529ad4b 100644
--- a/src/soc/mediatek/mt8192/include/soc/rtc.h
+++ b/src/soc/mediatek/mt8192/include/soc/rtc.h
@@ -85,7 +85,6 @@ enum {
 
 void rtc_read(u16 addr, u16 *rdata);
 void rtc_write(u16 addr, u16 wdata);
-void rtc_bbpu_power_on(void);
 int rtc_init(int recover);
 bool rtc_gpio_init(void);
 void rtc_boot(void);
diff --git a/src/soc/mediatek/mt8195/include/soc/rtc.h b/src/soc/mediatek/mt8195/include/soc/rtc.h
index 3dcb0ea968..342aadf776 100644
--- a/src/soc/mediatek/mt8195/include/soc/rtc.h
+++ b/src/soc/mediatek/mt8195/include/soc/rtc.h
@@ -85,7 +85,6 @@ enum {
 
 void rtc_read(u16 addr, u16 *rdata);
 void rtc_write(u16 addr, u16 wdata);
-void rtc_bbpu_power_on(void);
 int rtc_init(int recover);
 bool rtc_gpio_init(void);
 void rtc_boot(void);