diff --git a/stmhal/adc.c b/stmhal/adc.c
index 4930310fd3..c2419d543f 100644
--- a/stmhal/adc.c
+++ b/stmhal/adc.c
@@ -80,7 +80,7 @@ typedef struct _pyb_obj_adc_t {
     ADC_HandleTypeDef handle;
 } pyb_obj_adc_t;
 
-void adc_init_single(pyb_obj_adc_t *adc_obj) {
+STATIC void adc_init_single(pyb_obj_adc_t *adc_obj) {
     if (!IS_ADC_CHANNEL(adc_obj->channel)) {
         return;
     }
@@ -114,7 +114,9 @@ void adc_init_single(pyb_obj_adc_t *adc_obj) {
     adcHandle->Init.EOCSelection          = DISABLE;
 
     HAL_ADC_Init(adcHandle);
+}
 
+STATIC void adc_config_channel(pyb_obj_adc_t *adc_obj) {
     ADC_ChannelConfTypeDef sConfig;
 
     sConfig.Channel = adc_obj->channel;
@@ -122,10 +124,10 @@ void adc_init_single(pyb_obj_adc_t *adc_obj) {
     sConfig.SamplingTime = ADC_SAMPLETIME_15CYCLES;
     sConfig.Offset = 0;
 
-    HAL_ADC_ConfigChannel(adcHandle, &sConfig);
+    HAL_ADC_ConfigChannel(&adc_obj->handle, &sConfig);
 }
 
-uint32_t adc_read_channel(ADC_HandleTypeDef *adcHandle) {
+STATIC uint32_t adc_read_channel(ADC_HandleTypeDef *adcHandle) {
     uint32_t rawValue = 0;
 
     HAL_ADC_Start(adcHandle);
@@ -193,6 +195,7 @@ STATIC mp_obj_t adc_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const mp_
 STATIC mp_obj_t adc_read(mp_obj_t self_in) {
     pyb_obj_adc_t *self = self_in;
 
+    adc_config_channel(self);
     uint32_t data = adc_read_channel(&self->handle);
     return mp_obj_new_int(data);
 }
@@ -226,6 +229,7 @@ STATIC mp_obj_t adc_read_timed(mp_obj_t self_in, mp_obj_t buf_in, mp_obj_t freq_
 
     // This uses the timer in polling mode to do the sampling
     // We could use DMA, but then we can't convert the values correctly for the buffer
+    adc_config_channel(self);
     for (uint index = 0; index < bufinfo.len; index++) {
         // Wait for the timer to trigger
         while (__HAL_TIM_GET_FLAG(&TIM6_Handle, TIM_FLAG_UPDATE) == RESET) {