diff --git a/app/src/main/java/xdsopl/robot36/Decoder.java b/app/src/main/java/xdsopl/robot36/Decoder.java
index 0b527d4..9e56330 100644
--- a/app/src/main/java/xdsopl/robot36/Decoder.java
+++ b/app/src/main/java/xdsopl/robot36/Decoder.java
@@ -357,7 +357,6 @@ public class Decoder {
 			return false;
 		if (scanLineStdDev(lines, mean) > scanLineToleranceSamples)
 			return false;
-		float frequencyOffset = (float) frequencyOffsetMean(freqOffs);
 		boolean pictureChanged = false;
 		if (imageBuffer.line < 0 || imageBuffer.line >= imageBuffer.height) {
 			Mode prevMode = lastMode;
@@ -365,12 +364,15 @@ public class Decoder {
 			pictureChanged = lastMode != prevMode
 				|| Math.abs(lastScanLineSamples - scanLineSamples) > scanLineToleranceSamples
 				|| Math.abs(lastSyncPulseIndex + scanLineSamples - pulses[pulses.length - 1]) > syncPulseToleranceSamples;
+		} else if (Math.abs(scanLineSamples - lastMode.getScanLineSamples()) > scanLineToleranceSamples) {
+			return false;
 		}
 		if (pictureChanged) {
 			drawLines(0xff000000, 10);
 			drawLines(0xff00ffff, 8);
 			drawLines(0xff000000, 10);
 		}
+		float frequencyOffset = (float) frequencyOffsetMean(freqOffs);
 		if (pulses[0] >= scanLineSamples && pictureChanged) {
 			int endPulse = pulses[0];
 			int extrapolate = endPulse / scanLineSamples;