diff --git a/mantidimaging/gui/windows/spectrum_viewer/spectrum_widget.py b/mantidimaging/gui/windows/spectrum_viewer/spectrum_widget.py
index e9d0da14331..f7ff2cd6cf4 100644
--- a/mantidimaging/gui/windows/spectrum_viewer/spectrum_widget.py
+++ b/mantidimaging/gui/windows/spectrum_viewer/spectrum_widget.py
@@ -87,7 +87,7 @@ def __init__(self) -> None:
         self.nextRow()
         self.spectrum = self.addPlot()
 
-        self.spectrum_data_dict: dict[str, np.ndarray] = {}
+        self.spectrum_data_dict: dict[str, np.ndarray | None] = {}
         self.nextRow()
         self._tof_range_label = self.addLabel()
 
diff --git a/mantidimaging/gui/windows/spectrum_viewer/view.py b/mantidimaging/gui/windows/spectrum_viewer/view.py
index 778ed0d3cf0..cc34f436dc3 100644
--- a/mantidimaging/gui/windows/spectrum_viewer/view.py
+++ b/mantidimaging/gui/windows/spectrum_viewer/view.py
@@ -213,9 +213,7 @@ def set_spectrum(self, name: str, spectrum_data: 'np.ndarray'):
         self.spectrum.spectrum_data_dict[name] = spectrum_data
         self.spectrum.spectrum.clearPlots()
 
-        for key, value in self.spectrum.spectrum_data_dict.items():
-            if key in self.spectrum.roi_dict:
-                self.spectrum.spectrum.plot(value, name=key, pen=self.spectrum.roi_dict[key].colour)
+        self.show_visible_spectrums()
 
     def clear(self) -> None:
         self.spectrum.spectrum_data_dict = {}
@@ -256,14 +254,15 @@ def set_roi_alpha(self, alpha: float, roi_name: str) -> None:
         """
         self.spectrum.set_roi_alpha(roi_name, alpha)
         if alpha == 0:
-            self.spectrum.spectrum_data_dict[roi_name] = np.zeros(self.spectrum.spectrum_data_dict[roi_name].shape)
-        else:
-            self.spectrum.spectrum_data_dict[roi_name] = self.spectrum.spectrum_data_dict[roi_name]
+            self.spectrum.spectrum_data_dict[roi_name] = None
 
         self.spectrum.spectrum.clearPlots()
         self.spectrum.spectrum.update()
+        self.show_visible_spectrums()
+
+    def show_visible_spectrums(self):
         for key, value in self.spectrum.spectrum_data_dict.items():
-            if key in self.spectrum.roi_dict:
+            if value is not None and key in self.spectrum.roi_dict:
                 self.spectrum.spectrum.plot(value, name=key, pen=self.spectrum.roi_dict[key].colour)
 
     def add_roi_table_row(self, name: str, colour: tuple[int, int, int]):