diff --git a/components/driver/deprecated/adc_dma_legacy.c b/components/driver/deprecated/adc_dma_legacy.c
index d03bc67e24..7b1f135d20 100644
--- a/components/driver/deprecated/adc_dma_legacy.c
+++ b/components/driver/deprecated/adc_dma_legacy.c
@@ -104,7 +104,7 @@ static void adc_dma_intr_handler(void *arg);
 
 static int8_t adc_digi_get_io_num(adc_unit_t adc_unit, uint8_t adc_channel)
 {
-    assert(adc_unit <= SOC_ADC_PERIPH_NUM);
+    assert(adc_unit < SOC_ADC_PERIPH_NUM);
     uint8_t adc_n = (adc_unit == ADC_UNIT_1) ? 0 : 1;
     return adc_channel_io_map[adc_n][adc_channel];
 }