diff --git a/openmc/capi/filter.py b/openmc/capi/filter.py
index 5bd451b30..8d9d794d1 100644
--- a/openmc/capi/filter.py
+++ b/openmc/capi/filter.py
@@ -360,7 +360,7 @@ class ZernikeFilter(Filter):
         _dll.openmc_zernike_filter_set_order(self._index, order)
 
 
-class ZernikeRadialFilter(Filter):
+class ZernikeRadialFilter(ZernikeFilter):
     filter_type = 'zernikeradial'
 
 
diff --git a/src/tallies/tally_filter_zernike.F90 b/src/tallies/tally_filter_zernike.F90
index 73fda7fad..04515cf31 100644
--- a/src/tallies/tally_filter_zernike.F90
+++ b/src/tallies/tally_filter_zernike.F90
@@ -55,13 +55,13 @@ contains
 ! ZernikeFilter methods
 !===============================================================================
 
-  function calc_n_bins_zn(this) result(num_n_bins)
+  function calc_n_bins_zn(this) result(n_bins)
     class(ZernikeFilter), intent(in) :: this
     integer :: n
-    integer :: num_n_bins
+    integer :: n_bins
 
     n = this % order
-    num_n_bins = ((n+1) * (n+2))/2
+    n_bins = ((n+1) * (n+2))/2
   end function calc_n_bins_zn
 
   subroutine from_xml_zn(this, node)