diff --git a/os/hal/ports/STM32/LLD/ADCv4/hal_adc_lld.c b/os/hal/ports/STM32/LLD/ADCv4/hal_adc_lld.c
index d1a890515..812acd3ba 100644
--- a/os/hal/ports/STM32/LLD/ADCv4/hal_adc_lld.c
+++ b/os/hal/ports/STM32/LLD/ADCv4/hal_adc_lld.c
@@ -556,7 +556,7 @@ void adc_lld_stop(ADCDriver *adcp) {
  * @notapi
  */
 void adc_lld_start_conversion(ADCDriver *adcp) {
-  uint32_t dmamode, cfgr;
+  uint32_t dmamode, cfgr = 0U;
   const ADCConversionGroup *grpp = adcp->grpp;
 
 #if STM32_ADC_USE_ADC12 == TRUE
diff --git a/readme.txt b/readme.txt
index 36c6f2277..d97e5c333 100644
--- a/readme.txt
+++ b/readme.txt
@@ -134,6 +134,8 @@
        MEMS Accelerometers.
 - NEW: Safer messages mechanism for sandboxes (to be backported to 20.3.1).
 - NEW: Added latency measurement test application.
+- FIX: Fixed warning in STM32 ADCv4 (bug #1158)
+       (backported to 20.3.4)(backported to 19.1.5).
 - FIX: Fixed wrong check on HAL_USE_RTC in STM32G4 clock initialization
        (bug #1157)(backported to 20.3.4).
 - FIX: Fixed wrong checks related to PLLSAI2 on L4 and L4+ (bug #1156)