diff --git a/src/applications/gqrx/mainwindow.cpp b/src/applications/gqrx/mainwindow.cpp
index 2b6ce03a3c..bc8887a6ff 100644
--- a/src/applications/gqrx/mainwindow.cpp
+++ b/src/applications/gqrx/mainwindow.cpp
@@ -2136,6 +2136,7 @@ void MainWindow::iqFftTimeout()
     unsigned int    fftsize;
     unsigned int    i;
     qint64 fft_approx_timestamp;
+    qint64 fft_start=QDateTime::currentMSecsSinceEpoch();
 
     // FIXME: fftsize is a reference
     rx->get_iq_fft_data(d_fftData, fftsize);
@@ -2156,6 +2157,8 @@ void MainWindow::iqFftTimeout()
     }
 
     ui->plotter->setNewFftData(d_iirFftData, d_realFftData, fftsize, fft_approx_timestamp);
+    d_fft_duration+=(double(QDateTime::currentMSecsSinceEpoch()-fft_start)-d_fft_duration)*0.1;
+    uiDockFft->setFftLag(d_fft_duration>iq_fft_timer->interval());
 }
 
 void MainWindow::iqFftToMag(unsigned int fftsize, std::complex<float>* fftData, float* realFftData) const
diff --git a/src/applications/gqrx/mainwindow.h b/src/applications/gqrx/mainwindow.h
index 55e0e0b20d..c19c5917ce 100644
--- a/src/applications/gqrx/mainwindow.h
+++ b/src/applications/gqrx/mainwindow.h
@@ -145,6 +145,7 @@ public slots:
     std::condition_variable waterfall_background_ready;
     int waterfall_background_threads{0};
     std::thread waterfall_background_thread;
+    double d_fft_duration{0.0};
 
 private:
     void updateHWFrequencyRange(bool ignore_limits);
diff --git a/src/qtgui/dockfft.cpp b/src/qtgui/dockfft.cpp
index 723fa5b145..2f6cb4fc0e 100644
--- a/src/qtgui/dockfft.cpp
+++ b/src/qtgui/dockfft.cpp
@@ -636,6 +636,11 @@ void DockFft::on_threadsComboBox_currentTextChanged(const QString &text)
     emit wfThreadsChanged(val);
 }
 
+void DockFft::setFftLag(bool l)
+{
+    ui->fftRateLabel->setStyleSheet(l?"background:red;":"");
+}
+
 /** Update RBW and FFT overlab labels */
 void DockFft::updateInfoLabels(void)
 {
diff --git a/src/qtgui/dockfft.h b/src/qtgui/dockfft.h
index 131bbcc6ff..099aa70e85 100644
--- a/src/qtgui/dockfft.h
+++ b/src/qtgui/dockfft.h
@@ -46,6 +46,7 @@ class DockFft : public QDockWidget
     int setFftSize(int fft_size);
 
     void setSampleRate(float sample_rate);
+    void setFftLag(bool);
 
     void saveSettings(QSettings *settings);
     void readSettings(QSettings *settings);