diff --git a/rfg_adc_plotter/gui/pyqtgraph_backend.py b/rfg_adc_plotter/gui/pyqtgraph_backend.py
index 3b01411..8c79789 100644
--- a/rfg_adc_plotter/gui/pyqtgraph_backend.py
+++ b/rfg_adc_plotter/gui/pyqtgraph_backend.py
@@ -3172,11 +3172,14 @@ def run_pyqtgraph(args) -> None:
                     levels = compute_background_subtracted_bscan_levels(disp_fft_lin, disp_fft)
                 if levels is None:
                     try:
-                        mean_spec = np.nanmean(disp_fft, axis=1)
-                        vmin_v = float(np.nanmin(mean_spec))
-                        vmax_v = float(np.nanmax(mean_spec))
-                        if np.isfinite(vmin_v) and np.isfinite(vmax_v) and vmin_v != vmax_v:
-                            levels = (vmin_v, vmax_v)
+                        finite_rows = np.any(np.isfinite(disp_fft), axis=1)
+                        if np.any(finite_rows):
+                            mean_spec = np.nanmean(disp_fft[finite_rows], axis=1)
+                            if mean_spec.size > 0:
+                                vmin_v = float(np.nanmin(mean_spec))
+                                vmax_v = float(np.nanmax(mean_spec))
+                                if np.isfinite(vmin_v) and np.isfinite(vmax_v) and vmin_v != vmax_v:
+                                    levels = (vmin_v, vmax_v)
                     except Exception:
                         levels = None
                     if levels is None and spec_clip is not None: