diff --git a/firmware/mcp_adc.c b/firmware/mcp_adc.c
index 9aaa43d..ae531ae 100644
--- a/firmware/mcp_adc.c
+++ b/firmware/mcp_adc.c
@@ -40,15 +40,17 @@ void mcpadc_init(uint8_t mode)
 uint8_t mcpadc_has_new_data(void)
 {
 	/* this assumes that the first RDY bit read after the sample data indicates the old/new state of the sample we just read */
+#if ADC_ENABLE_18_BIT_MODE
 	if(curmode & ADC_BITS_MASK == ADC_BITS_18)
 	{
 		i2c_read(ADC_ADDR, 4, r);
-		curmode = r[4];
+		curmode = r[3];
 	}
 	else
+#endif
 	{
 		i2c_read(ADC_ADDR, 3, r);
-		curmode = r[3];
+		curmode = r[2];
 	}
 	if(~curmode & ADC_NEW_SAMPLE) {curmode &= ADC_READ_DATA;}
 	return ~curmode & ADC_READ_DATA;