diff --git a/drivers/adc/stm32-adc.c b/drivers/adc/stm32-adc.c
index e108062..029338e 100644
--- a/drivers/adc/stm32-adc.c
+++ b/drivers/adc/stm32-adc.c
@@ -163,15 +163,16 @@
 	struct adc_uclass_platdata *uc_pdata = dev_get_uclass_platdata(dev);
 	struct stm32_adc *adc = dev_get_priv(dev);
 	u32 chans[STM32_ADC_CH_MAX];
-	int i, num_channels, ret;
+	unsigned int i, num_channels;
+	int ret;
 
 	/* Retrieve single ended channels listed in device tree */
-	num_channels = dev_read_size(dev, "st,adc-channels");
-	if (num_channels < 0) {
-		dev_err(dev, "can't get st,adc-channels: %d\n", num_channels);
-		return num_channels;
+	ret = dev_read_size(dev, "st,adc-channels");
+	if (ret < 0) {
+		dev_err(dev, "can't get st,adc-channels: %d\n", ret);
+		return ret;
 	}
-	num_channels /= sizeof(u32);
+	num_channels = ret / sizeof(u32);
 
 	if (num_channels > adc->cfg->max_channels) {
 		dev_err(dev, "too many st,adc-channels: %d\n", num_channels);