diff --git a/boards/common/blxxxpill/include/periph_conf.h b/boards/common/blxxxpill/include/periph_conf.h
index 143b69a82a..7cf572a8a2 100644
--- a/boards/common/blxxxpill/include/periph_conf.h
+++ b/boards/common/blxxxpill/include/periph_conf.h
@@ -74,9 +74,13 @@ extern "C" {
     { .dev = 0, .pin = GPIO_PIN(PORT_A, 7), .chan = 7 }, \
     { .dev = 0, .pin = GPIO_PIN(PORT_B, 0), .chan = 8 }, \
     { .dev = 0, .pin = GPIO_PIN(PORT_B, 1), .chan = 9 }, \
+    /* ADC Temperature channel */                        \
+    { .dev = 0, .pin = GPIO_UNDEF, .chan = 16 },         \
+    /* ADC VREF channel */                               \
+    { .dev = 0, .pin = GPIO_UNDEF, .chan = 17 },         \
 }
 
-#define ADC_NUMOF           10
+#define ADC_NUMOF           12
 /** @} */
 
 /**
diff --git a/cpu/stm32f1/periph/adc.c b/cpu/stm32f1/periph/adc.c
index 2c68df9430..270547bdf9 100644
--- a/cpu/stm32f1/periph/adc.c
+++ b/cpu/stm32f1/periph/adc.c
@@ -57,10 +57,22 @@ static inline void prep(adc_t line)
 {
     mutex_lock(&locks[adc_config[line].dev]);
     periph_clk_en(APB2, (RCC_APB2ENR_ADC1EN << adc_config[line].dev));
+
+    /* check if this channel is an internal ADC channel, if so
+     * enable the internal temperature and Vref */
+    if (adc_config[line].chan == 16 || adc_config[line].chan == 17) {
+        dev(line)->CR2 |= ADC_CR2_TSVREFE;
+    }
 }
 
 static inline void done(adc_t line)
 {
+    /* check if this channel is an internal ADC channel, if so
+     * disable the internal temperature and Vref */
+    if (adc_config[line].chan == 16 || adc_config[line].chan == 17) {
+        dev(line)->CR2 &= ~ADC_CR2_TSVREFE;
+    }
+
     periph_clk_dis(APB2, (RCC_APB2ENR_ADC1EN << adc_config[line].dev));
     mutex_unlock(&locks[adc_config[line].dev]);
 }
@@ -78,7 +90,9 @@ int adc_init(adc_t line)
     prep(line);
 
     /* configure the pin */
-    gpio_init_analog(adc_config[line].pin);
+    if (adc_config[line].pin != GPIO_UNDEF) {
+        gpio_init_analog(adc_config[line].pin);
+    }
     /* set clock prescaler to get the maximal possible ADC clock value */
     for (clk_div = 2; clk_div < 8; clk_div += 2) {
         if ((CLOCK_CORECLOCK / clk_div) <= MAX_ADC_SPEED) {
@@ -109,15 +123,11 @@ int adc_init(adc_t line)
     /* start sampling from software */
     dev(line)->CR2 |= ADC_CR2_EXTTRIG | ADC_CR2_EXTSEL;
 
-    /* check if this channel is an internal ADC channel, if so
-     * enable the internal temperature and Vref */
+    /* check if the internal channels are configured to use ADC1 */
     if (adc_config[line].chan == 16 || adc_config[line].chan == 17) {
-        /* check if the internal channels are configured to use ADC1 */
         if (dev(line) != ADC1) {
             return -3;
         }
-
-        dev(line)->CR2 |= ADC_CR2_TSVREFE;
     }
 
     /* free the device again */