diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5cd748f6984..dc2c2e0b934 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 - [[PR564]](https://github.com/lanl/singularity-eos/pull/564) Removed Get() function from IndexableTypes since it could have unexpected consequences when a type wasn't present
 
 ### Fixed (Repair bugs, etc)
+- [[PR567]](https://github.com/lanl/singularity-eos/pull/567) Fixed an OOB array access bug in the Fixed T PTE solver
 - [[PR561]](https://github.com/lanl/singularity-eos/pull/561) Fix logic for kokkos-kernels in spackage so that it is only required for closure models on GPU
 - [[PR563]](https://github.com/lanl/singularity-eos/pull/563) Fixed DensityFromPressureTemperature for the Carnahan-Starling EOS.
 - [[PR564]](https://github.com/lanl/singularity-eos/pull/564) Fix logic for numerical vs type indices by adding safeGet(), safeSet(), safeMustGet(), and safeMustSet() helpers
diff --git a/singularity-eos/closure/mixed_cell_models.hpp b/singularity-eos/closure/mixed_cell_models.hpp
index fecd8938f7f..c4b1238193d 100644
--- a/singularity-eos/closure/mixed_cell_models.hpp
+++ b/singularity-eos/closure/mixed_cell_models.hpp
@@ -1455,7 +1455,7 @@ class PTESolverFixedT
     Real error_p = 0;
     for (std::size_t m = 1; m < nmat; ++m) {
       mean_p += vfrac[m] * press[m];
-      error_p += residual[m + 1] * residual[m + 1];
+      error_p += residual[m] * residual[m];
     }
     error_p = std::sqrt(error_p);
     Real error_v = std::abs(residual[0]);