diff --git a/docs/source/pythonapi/index.rst b/docs/source/pythonapi/index.rst
index 14f4a2128..d8eb5200a 100644
--- a/docs/source/pythonapi/index.rst
+++ b/docs/source/pythonapi/index.rst
@@ -298,6 +298,7 @@ Multi-delayed-group Cross Sections
     openmc.mgxs.ChiDelayed
     openmc.mgxs.DelayedNuFissionXS
     openmc.mgxs.Beta
+    openmc.mgxs.DecayRate
 
 Multi-group Cross Section Libraries
 -----------------------------------
diff --git a/openmc/mgxs/mdgxs.py b/openmc/mgxs/mdgxs.py
index 9fa286ff3..69b20d3f4 100644
--- a/openmc/mgxs/mdgxs.py
+++ b/openmc/mgxs/mdgxs.py
@@ -1602,9 +1602,9 @@ class DecayRate(MDGXS):
     .. math::
 
        \langle \lambda_d \nu^d \sigma_f \phi \rangle &= \int_{r \in V} dr
-       \int_{4\pi} d\Omega' \int_0^\infty dE' \int_0^\infty dE \; \chi(E) \nu^d
+       \int_{4\pi} d\Omega' \int_0^\infty dE' \int_0^\infty dE \; \lambda_d \nu^d
        \sigma_f (r, E') \psi(r, E', \Omega') \\
-       \langle \nu \sigma_f \phi \rangle &= \int_{r \in V} dr \int_{4\pi}
+       \langle \nu^d \sigma_f \phi \rangle &= \int_{r \in V} dr \int_{4\pi}
        d\Omega' \int_0^\infty dE' \int_0^\infty dE \; \chi(E) \nu^d
        \sigma_f (r, E') \psi(r, E', \Omega') \\
        \lambda_d &= \frac{\langle \lambda_d \nu^d \sigma_f \phi \rangle}
diff --git a/src/tally.F90 b/src/tally.F90
index 542e1ff5c..c0e8013a3 100644
--- a/src/tally.F90
+++ b/src/tally.F90
@@ -708,7 +708,7 @@ contains
                     score = p % absorb_wgt * yield * &
                          micro_xs(p % event_nuclide) % fission &
                          / micro_xs(p % event_nuclide) % absorption &
-                         * rxn % products(1 + d) % decay_rate * 1.e8
+                         * rxn % products(1 + d) % decay_rate * 1.e8_8
                   end associate
 
                   ! Tally to bin
@@ -733,7 +733,7 @@ contains
                 ! and not the MAX_DELAYED_GROUPS constant for this loop.
                 do d = 1, size(rxn % products) - 2
 
-                  score = score + rxn % products(1 + d) % decay_rate * 1.e8 * &
+                  score = score + rxn % products(1 + d) % decay_rate * 1.e8_8 * &
                        p % absorb_wgt * micro_xs(p % event_nuclide) % fission *&
                        nuclides(p % event_nuclide) % nu(E, EMISSION_DELAYED, d)&
                        / micro_xs(p % event_nuclide) % absorption
@@ -773,7 +773,7 @@ contains
                 ! the units of the decay rate have been converted from inverse
                 ! shakes to inverse seconds (1 shake = 1.e-8 seconds)
                 score = score + keff * fission_bank(n_bank - p % n_bank + k) &
-                     % wgt * rxn % products(1 + g) % decay_rate * 1.e8
+                     % wgt * rxn % products(1 + g) % decay_rate * 1.e8_8
               end associate
 
               ! if the delayed group filter is present, tally to corresponding