diff --git a/app/src/main/java/xdsopl/robot36/Decoder.java b/app/src/main/java/xdsopl/robot36/Decoder.java
index c7ed696..aee26d5 100644
--- a/app/src/main/java/xdsopl/robot36/Decoder.java
+++ b/app/src/main/java/xdsopl/robot36/Decoder.java
@@ -145,14 +145,17 @@ public class Decoder {
 		}
 		for (int i = 0; i < lines.length; ++i)
 			copyLines(mode.decodeScanLine(evenBuffer, oddBuffer, scanLineBuffer, pulses[i], lines[i]));
-		int shift = pulses[pulses.length - 1] - (meanSamples * 3) / 4;
-		adjustSyncPulses(last5msSyncPulses, shift);
-		adjustSyncPulses(last9msSyncPulses, shift);
-		adjustSyncPulses(last20msSyncPulses, shift);
-		int endSample = curSample;
-		curSample = 0;
-		for (int i = shift; i < endSample; ++i)
-			scanLineBuffer[curSample++] = scanLineBuffer[i];
+		int reserve = (meanSamples * 3) / 4;
+		int shift = pulses[pulses.length - 1] - reserve;
+		if (shift > reserve) {
+			adjustSyncPulses(last5msSyncPulses, shift);
+			adjustSyncPulses(last9msSyncPulses, shift);
+			adjustSyncPulses(last20msSyncPulses, shift);
+			int endSample = curSample;
+			curSample = 0;
+			for (int i = shift; i < endSample; ++i)
+				scanLineBuffer[curSample++] = scanLineBuffer[i];
+		}
 		return true;
 	}