diff --git a/plugins/samplesource/rtlsdr/rtlsdrthread.cpp b/plugins/samplesource/rtlsdr/rtlsdrthread.cpp
index 778d5acfa..8346668c7 100644
--- a/plugins/samplesource/rtlsdr/rtlsdrthread.cpp
+++ b/plugins/samplesource/rtlsdr/rtlsdrthread.cpp
@@ -77,7 +77,7 @@ void RTLSDRThread::run()
 void RTLSDRThread::decimate2(SampleVector::iterator* it, const quint8* buf, qint32 len)
 {
 	qint16 xreal, yimag;
-	for (int pos = 0; pos < len + 7; pos += 8) {
+	for (int pos = 0; pos < len - 7; pos += 8) {
 		xreal = buf[pos+0] - buf[pos+3];
 		yimag = buf[pos+1] + buf[pos+2] - 255;
 		Sample s( xreal << 3, yimag << 3 );
@@ -93,7 +93,7 @@ void RTLSDRThread::decimate2(SampleVector::iterator* it, const quint8* buf, qint
 void RTLSDRThread::decimate4(SampleVector::iterator* it, const quint8* buf, qint32 len)
 {
 	qint16 xreal, yimag;
-		for (int pos = 0; pos < len + 7; pos += 8) {
+		for (int pos = 0; pos < len - 7; pos += 8) {
 		xreal = buf[pos+0] - buf[pos+3] + buf[pos+7] - buf[pos+4];
 		yimag = buf[pos+1] - buf[pos+5] + buf[pos+2] - buf[pos+6];
 		Sample s( xreal << 4, yimag << 4 );
@@ -105,7 +105,7 @@ void RTLSDRThread::decimate4(SampleVector::iterator* it, const quint8* buf, qint
 void RTLSDRThread::decimate8(SampleVector::iterator* it, const quint8* buf, qint32 len)
 {
 	qint16 xreal, yimag;
-	for (int pos = 0; pos < len + 15; pos += 8) {
+	for (int pos = 0; pos < len - 15; pos += 8) {
 		xreal = buf[pos+0] - buf[pos+3] + buf[pos+7] - buf[pos+4];
 		yimag = buf[pos+1] - buf[pos+5] + buf[pos+2] - buf[pos+6];
 		pos += 8;