diff --git a/os/hal/ports/STM32/STM32L1xx/hal_adc_lld.c b/os/hal/ports/STM32/STM32L1xx/hal_adc_lld.c
index b61a73d20..78c000186 100644
--- a/os/hal/ports/STM32/STM32L1xx/hal_adc_lld.c
+++ b/os/hal/ports/STM32/STM32L1xx/hal_adc_lld.c
@@ -224,7 +224,7 @@ void adc_lld_start_conversion(ADCDriver *adcp) {
 
   /* ADC setup.*/
   adcp->adc->SR    = 0;
-  adcp->adc->SMPR1 = grpp->smpr1;
+  adcp->adc->SMPR1 = grpp->smpr1 | ADC_SQR1_NUM_CH(grpp->num_channels);
   adcp->adc->SMPR2 = grpp->smpr2;
   adcp->adc->SMPR3 = grpp->smpr3;
   adcp->adc->SQR1  = grpp->sqr1;
diff --git a/readme.txt b/readme.txt
index 3ab56c917..43653b51d 100644
--- a/readme.txt
+++ b/readme.txt
@@ -131,6 +131,8 @@
 - NEW: Increased stacks size in RT test suite from 128 to 192. added an
        option to override the stack size by defining THREADS_STACK_SIZE
        in the makefile.
+- FIX: Fixed wrong initialization in STM32L1xx ADC driver (bug #1247)
+       (backported to 20.3.5)(backported to 21.11.3).
 - FIX: Fixed wrong HSI48 support on STM32L0xx (bug #1246)
        (backported to 20.3.5)(backported to 21.11.3).
 - FIX: Fixed wrong DMA definitions for STM32L0xx I2C3 peripheral (bug #1245)