diff --git a/src/serpentTools/detectors.py b/src/serpentTools/detectors.py
index 54e37d4d..b094ba35 100644
--- a/src/serpentTools/detectors.py
+++ b/src/serpentTools/detectors.py
@@ -567,10 +567,11 @@ def spectrumPlot(
         elif len(slicedTallies.shape) == 1:
             slicedTallies = slicedTallies.reshape(slicedTallies.size, 1)
 
+        # (n_groups, 3) where columns are lower, upper, and middle energy
         lowerE = self.grids['E'][:, 0]
         if normalize:
             lethBins = log(
-                divide(self.grids['E'][:, -1], lowerE))
+                divide(self.grids['E'][:, 1], lowerE))
             # Need to scale up the dimension of the energy grids to support
             # broadcasting -> (E, N) / (E, )
             slicedTallies /= lethBins[:, newaxis]
diff --git a/tests/plots/result_images/testSpectrumJustNormPerLethargy.png b/tests/plots/result_images/testSpectrumJustNormPerLethargy.png
index 4ee25714..62e6f009 100644
Binary files a/tests/plots/result_images/testSpectrumJustNormPerLethargy.png and b/tests/plots/result_images/testSpectrumJustNormPerLethargy.png differ
diff --git a/tests/plots/result_images/testSpectrumPlot.png b/tests/plots/result_images/testSpectrumPlot.png
index 2528ea2d..bf746712 100644
Binary files a/tests/plots/result_images/testSpectrumPlot.png and b/tests/plots/result_images/testSpectrumPlot.png differ