diff --git a/flang/lib/Lower/ConvertExpr.cpp b/flang/lib/Lower/ConvertExpr.cpp
index fdb6291b8e6c4..6c493024bd1cb 100644
--- a/flang/lib/Lower/ConvertExpr.cpp
+++ b/flang/lib/Lower/ConvertExpr.cpp
@@ -2558,7 +2558,7 @@ class ScalarExprLowering {
           // callee side, and it is illegal to use NULL without a MOLD if any
           // dummy length parameters are assumed.
           mlir::Type boxTy = fir::dyn_cast_ptrEleTy(argTy);
-          assert(boxTy && boxTy.isa<fir::BoxType>() &&
+          assert(boxTy && boxTy.isa<fir::BaseBoxType>() &&
                  "must be a fir.box type");
           mlir::Value boxStorage = builder.createTemporary(loc, boxTy);
           mlir::Value nullBox = fir::factory::createUnallocatedBox(
diff --git a/flang/test/Lower/polymorphic.f90 b/flang/test/Lower/polymorphic.f90
index 52e4498a8d765..fe6ae879c540c 100644
--- a/flang/test/Lower/polymorphic.f90
+++ b/flang/test/Lower/polymorphic.f90
@@ -824,6 +824,21 @@ subroutine sub_with_real_pointer_optional(p)
 ! CHECK: }
 ! CHECK: fir.call @_QMpolymorphic_testPsub_with_poly_array_optional(%[[BOX]]) {{.*}} : (!fir.class<!fir.array<?xnone>>) -> ()
 
+  subroutine pass_poly_pointer_optional(p)
+    class(p1), pointer, optional :: p
+  end subroutine
+
+  subroutine test_poly_pointer_null()
+    call pass_poly_pointer_optional(null())
+  end subroutine
+
+! CHECK-LABEL: func.func @_QMpolymorphic_testPtest_poly_pointer_null() {
+! CHECK: %[[ALLOCA:.*]] = fir.alloca !fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>
+! CHECK: %[[ZERO:.*]] = fir.zero_bits !fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>
+! CHECK: %[[EMBOX:.*]] = fir.embox %[[ZERO]] : (!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>) -> !fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>
+! CHECK: fir.store %[[EMBOX]] to %[[ALLOCA]] : !fir.ref<!fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>
+! CHECK: fir.call @_QMpolymorphic_testPpass_poly_pointer_optional(%[[ALLOCA]]) fastmath<contract> : (!fir.ref<!fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>) -> ()
+
 end module
 
 program test