diff --git a/src/shearwater_predator_parser.c b/src/shearwater_predator_parser.c
index 3e5fcbf..e922220 100644
--- a/src/shearwater_predator_parser.c
+++ b/src/shearwater_predator_parser.c
@@ -448,14 +448,15 @@ shearwater_predator_parser_samples_foreach (dc_parser_t *abstract, dc_sample_cal
 			sample.ppo2 = data[offset + 6] / 100.0;
 			if (callback) callback (DC_SAMPLE_PPO2, sample, userdata);
 #else
-			sample.ppo2 = data[offset + 12] * parser->calibration[0];
-			if (callback && (data[86] & 0x01)) callback (DC_SAMPLE_PPO2, sample, userdata);
+			if ((status & PPO2_EXTERNAL) == 0) {
+				sample.ppo2 = data[offset + 12] * parser->calibration[0];
+				if (callback && (data[86] & 0x01)) callback (DC_SAMPLE_PPO2, sample, userdata);
 
-			sample.ppo2 = data[offset + 14] * parser->calibration[1];
-			if (callback && (data[86] & 0x02)) callback (DC_SAMPLE_PPO2, sample, userdata);
+				sample.ppo2 = data[offset + 14] * parser->calibration[1];
+				if (callback && (data[86] & 0x02)) callback (DC_SAMPLE_PPO2, sample, userdata);
 
-			sample.ppo2 = data[offset + 15] * parser->calibration[2];
-			if (callback && (data[86] & 0x04)) callback (DC_SAMPLE_PPO2, sample, userdata);
+				sample.ppo2 = data[offset + 15] * parser->calibration[2];
+				if (callback && (data[86] & 0x04)) callback (DC_SAMPLE_PPO2, sample, userdata);
 			}
 #endif