diff --git a/src/nuclide_header.F90 b/src/nuclide_header.F90
index 78d436bdd..4308bc487 100644
--- a/src/nuclide_header.F90
+++ b/src/nuclide_header.F90
@@ -703,15 +703,13 @@ contains
   end function openmc_nuclide_name
 
   subroutine extend_nuclides() bind(C)
-    integer :: n
     type(Nuclide), allocatable :: new_nuclides(:)
 
     ! allocate extra space in nuclides array
-    n = n_nuclides
-    allocate(new_nuclides(n + 1))
-    new_nuclides(1:n) = nuclides(:)
+    allocate(new_nuclides(n_nuclides + 1))
+    new_nuclides(1:n_nuclides) = nuclides(:)
     call move_alloc(FROM=new_nuclides, TO=nuclides)
-    n = n + 1
+    n_nuclides = n_nuclides + 1
   end subroutine
 
 end module nuclide_header
diff --git a/tests/unit_tests/test_capi.py b/tests/unit_tests/test_capi.py
index f5185e23f..420cffc4f 100644
--- a/tests/unit_tests/test_capi.py
+++ b/tests/unit_tests/test_capi.py
@@ -131,6 +131,7 @@ def test_nuclide_mapping(capi_init):
 
 
 def test_load_nuclide(capi_init):
+    openmc.capi.load_nuclide('H3')
     openmc.capi.load_nuclide('Pu239')
     with pytest.raises(exc.DataError):
         openmc.capi.load_nuclide('Pu3')