diff --git a/boards/b-l475e-iot01a/include/periph_conf.h b/boards/b-l475e-iot01a/include/periph_conf.h
index 65c79b52d1..d9046914ee 100644
--- a/boards/b-l475e-iot01a/include/periph_conf.h
+++ b/boards/b-l475e-iot01a/include/periph_conf.h
@@ -179,6 +179,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR1_I2C1EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C1SEL_1,          /* HSI (16 MHz) */
         .irqn           = I2C1_ER_IRQn,
     },
     {
@@ -190,6 +191,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR1_I2C2EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C2SEL_1,          /* HSI (16 MHz) */
         .irqn           = I2C2_ER_IRQn,
     },
 };
diff --git a/boards/b-u585i-iot02a/include/periph_conf.h b/boards/b-u585i-iot02a/include/periph_conf.h
index c7de49c36c..19a2795e81 100644
--- a/boards/b-u585i-iot02a/include/periph_conf.h
+++ b/boards/b-u585i-iot02a/include/periph_conf.h
@@ -158,6 +158,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR1_I2C1EN,
+        .rcc_sw_mask    = RCC_CCIPR1_I2C1SEL_1,
         .irqn           = I2C1_ER_IRQn,
     },
     {
@@ -169,6 +170,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR1_I2C2EN,
+        .rcc_sw_mask    = RCC_CCIPR1_I2C2SEL_1,
         .irqn           = I2C2_ER_IRQn,
     },
 };
diff --git a/boards/common/stm32/include/cfg_i2c1_pb6_pb7.h b/boards/common/stm32/include/cfg_i2c1_pb6_pb7.h
index 6e8f9c3ce5..cf239ba619 100644
--- a/boards/common/stm32/include/cfg_i2c1_pb6_pb7.h
+++ b/boards/common/stm32/include/cfg_i2c1_pb6_pb7.h
@@ -45,6 +45,7 @@ static const i2c_conf_t i2c_config[] = {
         .bus            = APB1,
 #if CPU_FAM_STM32L4
         .rcc_mask       = RCC_APB1ENR1_I2C1EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C1SEL_1,          /* HSI (16 MHz) */
         .irqn           = I2C1_ER_IRQn,
 #else /* CPU_FAM_STM32L0 */
         .rcc_mask       = RCC_APB1ENR_I2C1EN,
diff --git a/boards/common/stm32/include/cfg_i2c1_pb8_pb9.h b/boards/common/stm32/include/cfg_i2c1_pb8_pb9.h
index 985411f1c3..65499e8823 100644
--- a/boards/common/stm32/include/cfg_i2c1_pb8_pb9.h
+++ b/boards/common/stm32/include/cfg_i2c1_pb8_pb9.h
@@ -50,14 +50,21 @@ static const i2c_conf_t i2c_config[] = {
         .rcc_mask       = RCC_APB1ENR_I2C1EN,
         .clk            = CLOCK_APB1,
         .irqn           = I2C1_EV_IRQn,
-#elif CPU_FAM_STM32L4 || CPU_FAM_STM32WB || CPU_FAM_STM32G4 || CPU_FAM_STM32L5
+#elif CPU_FAM_STM32L4 || CPU_FAM_STM32WB || CPU_FAM_STM32G4
         .rcc_mask       = RCC_APB1ENR1_I2C1EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C1SEL_1,          /* HSI (16 MHz) */
+        .irqn           = I2C1_ER_IRQn,
+#elif CPU_FAM_STM32L5
+        .rcc_mask       = RCC_APB1ENR1_I2C1EN,
+        .rcc_sw_mask    = RCC_CCIPR1_I2C1SEL_1,         /* HSI (16 MHz) */
         .irqn           = I2C1_ER_IRQn,
 #elif CPU_FAM_STM32G0
         .rcc_mask       = RCC_APBENR1_I2C1EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C1SEL_1,          /* HSI (16 MHz) */
         .irqn           = I2C1_IRQn,
 #elif CPU_FAM_STM32F7
         .rcc_mask       = RCC_APB1ENR_I2C1EN,
+        .rcc_sw_mask    = RCC_DCKCFGR2_I2C1SEL_1,       /* HSI (16 MHz) */
         .irqn           = I2C1_ER_IRQn,
 #elif CPU_FAM_STM32F0 || CPU_FAM_STM32L0
         .rcc_mask       = RCC_APB1ENR_I2C1EN,
diff --git a/boards/lora-e5-dev/include/periph_conf.h b/boards/lora-e5-dev/include/periph_conf.h
index 4df678de62..e123e92d9c 100644
--- a/boards/lora-e5-dev/include/periph_conf.h
+++ b/boards/lora-e5-dev/include/periph_conf.h
@@ -143,6 +143,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR1_I2C2EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C2SEL_1,      /* HSI (16 MHz) */
         .irqn           = I2C2_ER_IRQn,
     }
 };
diff --git a/boards/nucleo-l433rc/include/periph_conf.h b/boards/nucleo-l433rc/include/periph_conf.h
index 9afa75259d..c704ba14af 100644
--- a/boards/nucleo-l433rc/include/periph_conf.h
+++ b/boards/nucleo-l433rc/include/periph_conf.h
@@ -131,6 +131,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR1_I2C1EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C2SEL_1,  /* HSI (16 MHz) */
         .irqn           = I2C1_ER_IRQn
     },
 };
diff --git a/boards/nucleo-wl55jc/include/periph_conf.h b/boards/nucleo-wl55jc/include/periph_conf.h
index 89156bd782..d8f7dbbca0 100644
--- a/boards/nucleo-wl55jc/include/periph_conf.h
+++ b/boards/nucleo-wl55jc/include/periph_conf.h
@@ -132,6 +132,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR1_I2C2EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C2SEL_1,  /* HSI (16 MHz) */
         .irqn           = I2C2_ER_IRQn,
     }
 };
diff --git a/boards/p-l496g-cell02/include/periph_conf.h b/boards/p-l496g-cell02/include/periph_conf.h
index d02b48b945..d4e78d90b8 100644
--- a/boards/p-l496g-cell02/include/periph_conf.h
+++ b/boards/p-l496g-cell02/include/periph_conf.h
@@ -116,6 +116,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR1_I2C1EN,
+        .rcc_sw_mask    = RCC_CCIPR_I2C1SEL_1,      /* HSI (16 MHz) */
         .irqn           = I2C1_ER_IRQn
     },
 };
diff --git a/boards/stm32f723e-disco/include/periph_conf.h b/boards/stm32f723e-disco/include/periph_conf.h
index ea1c4d58e4..28e4e7b5ed 100644
--- a/boards/stm32f723e-disco/include/periph_conf.h
+++ b/boards/stm32f723e-disco/include/periph_conf.h
@@ -154,6 +154,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR_I2C2EN,
+        .rcc_sw_mask    = RCC_DCKCFGR2_I2C2SEL_1,
         .irqn           = I2C2_ER_IRQn,
     },
     {   /* Connected to touchscreen controller */
@@ -165,6 +166,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR_I2C3EN,
+        .rcc_sw_mask    = RCC_DCKCFGR2_I2C3SEL_1,
         .irqn           = I2C3_ER_IRQn,
     },
     {
@@ -176,6 +178,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR_I2C1EN,
+        .rcc_sw_mask    = RCC_DCKCFGR2_I2C1SEL_1,
         .irqn           = I2C1_ER_IRQn,
     },
 };
diff --git a/boards/stm32f746g-disco/include/periph_conf.h b/boards/stm32f746g-disco/include/periph_conf.h
index 35dd80691b..07c671ce7c 100644
--- a/boards/stm32f746g-disco/include/periph_conf.h
+++ b/boards/stm32f746g-disco/include/periph_conf.h
@@ -160,6 +160,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR_I2C1EN,
+        .rcc_sw_mask    = RCC_DCKCFGR2_I2C1SEL_1,
         .irqn           = I2C1_ER_IRQn,
     },
     {
@@ -171,6 +172,7 @@ static const i2c_conf_t i2c_config[] = {
         .sda_af         = GPIO_AF4,
         .bus            = APB1,
         .rcc_mask       = RCC_APB1ENR_I2C3EN,
+        .rcc_sw_mask    = RCC_DCKCFGR2_I2C3SEL_1,
         .irqn           = I2C3_ER_IRQn,
     },
 };