diff --git a/arch/arm/src/stm32/stm32_eth.c b/arch/arm/src/stm32/stm32_eth.c
index e9c38e06286..e50a82d61d6 100644
--- a/arch/arm/src/stm32/stm32_eth.c
+++ b/arch/arm/src/stm32/stm32_eth.c
@@ -3355,6 +3355,7 @@ static inline void stm32_selectmii(void)
  *
  ****************************************************************************/
 
+#ifdef CONFIG_STM32_RMII
 static inline void stm32_selectrmii(void)
 {
   uint32_t regval;
@@ -3369,6 +3370,7 @@ static inline void stm32_selectrmii(void)
   putreg32(regval, STM32_SYSCFG_PMC);
 #endif
 }
+#endif
 
 /****************************************************************************
  * Function: stm32_ethgpioconfig
diff --git a/arch/arm/src/stm32f7/stm32_ethernet.c b/arch/arm/src/stm32f7/stm32_ethernet.c
index b16c578cc74..c82b703d813 100644
--- a/arch/arm/src/stm32f7/stm32_ethernet.c
+++ b/arch/arm/src/stm32f7/stm32_ethernet.c
@@ -3443,6 +3443,7 @@ static inline void stm32_selectmii(void)
  *
  ****************************************************************************/
 
+#ifdef CONFIG_STM32F7_RMII
 static inline void stm32_selectrmii(void)
 {
   uint32_t regval;
@@ -3451,6 +3452,7 @@ static inline void stm32_selectrmii(void)
   regval |= SYSCFG_PMC_MII_RMII_SEL;
   putreg32(regval, STM32_SYSCFG_PMC);
 }
+#endif
 
 /****************************************************************************
  * Function: stm32_ethgpioconfig
diff --git a/arch/arm/src/stm32h7/stm32_ethernet.c b/arch/arm/src/stm32h7/stm32_ethernet.c
index 6ff98cdc632..52524a02ccf 100644
--- a/arch/arm/src/stm32h7/stm32_ethernet.c
+++ b/arch/arm/src/stm32h7/stm32_ethernet.c
@@ -3616,6 +3616,7 @@ static inline void stm32_selectmii(void)
  *
  ****************************************************************************/
 
+#ifdef CONFIG_STM32H7_RMII
 static inline void stm32_selectrmii(void)
 {
   uint32_t regval;
@@ -3625,6 +3626,7 @@ static inline void stm32_selectrmii(void)
   regval |= SYSCFG_PMC_EPIS_RMII;
   putreg32(regval, STM32_SYSCFG_PMC);
 }
+#endif
 
 /****************************************************************************
  * Function: stm32_ethgpioconfig