diff --git a/include/openmc/xsdata.h b/include/openmc/xsdata.h
index a629d786af..a8aed5d17c 100644
--- a/include/openmc/xsdata.h
+++ b/include/openmc/xsdata.h
@@ -77,7 +77,7 @@ class XsData {
     // [angle][delayed group]
     xt::xtensor<double, 2> decay_rate;
     // delayed_nu_fission has the following dimensions:
-    // [angle][incoming group][delayed group]
+    // [angle][delayed group][incoming group]
     xt::xtensor<double, 3> delayed_nu_fission;
     // chi_prompt has the following dimensions:
     // [angle][incoming group][outgoing group]
diff --git a/src/mgxs.cpp b/src/mgxs.cpp
index 43554f5735..08c4f78941 100644
--- a/src/mgxs.cpp
+++ b/src/mgxs.cpp
@@ -467,7 +467,7 @@ Mgxs::get_xs(int xstype, int gin, int* gout, double* mu, int* dg)
         val = xs_t->delayed_nu_fission(a, *dg, gin);
       } else {
         val = 0.;
-        for (int d = 0; d < xs_t->delayed_nu_fission.shape()[2]; d++) {
+        for (int d = 0; d < xs_t->delayed_nu_fission.shape()[1]; d++) {
           val += xs_t->delayed_nu_fission(a, d, gin);
         }
       }