diff --git a/tests/test_fixed_source/materials.xml b/tests/test_fixed_source/materials.xml
index 5242021d3..ab7a76bc0 100644
--- a/tests/test_fixed_source/materials.xml
+++ b/tests/test_fixed_source/materials.xml
@@ -4,6 +4,7 @@
   <material id="1">
     <density value="7.5" units="g/cc" />
     <nuclide name="O-16" xs="71c" ao="1.0" />
+    <nuclide name="U-238" xs="71c" ao="0.0001" />
   </material>
 
 </materials>
diff --git a/tests/test_fixed_source/results_true.dat b/tests/test_fixed_source/results_true.dat
index 094030188..b3def050e 100644
--- a/tests/test_fixed_source/results_true.dat
+++ b/tests/test_fixed_source/results_true.dat
@@ -1,6 +1,6 @@
 tally 1:
-4.538791E+02
-2.073271E+04
+4.563929E+02
+2.091711E+04
 leakage:
-9.830000E+00
-9.663900E+00
+9.780000E+00
+9.566400E+00