diff --git a/flang/lib/Optimizer/Builder/FIRBuilder.cpp b/flang/lib/Optimizer/Builder/FIRBuilder.cpp
--- a/flang/lib/Optimizer/Builder/FIRBuilder.cpp
+++ b/flang/lib/Optimizer/Builder/FIRBuilder.cpp
@@ -1153,10 +1153,11 @@
                                                    fromCoor, indices);
     }
     if (auto fieldEleTy = fir::unwrapSequenceType(lFieldTy);
-        fieldEleTy.isa<fir::BoxType>()) {
-      assert(
-          fieldEleTy.cast<fir::BoxType>().getEleTy().isa<fir::PointerType>() &&
-          "allocatable members require deep copy");
+        fieldEleTy.isa<fir::BaseBoxType>()) {
+      assert(fieldEleTy.cast<fir::BaseBoxType>()
+                 .getEleTy()
+                 .isa<fir::PointerType>() &&
+             "allocatable members require deep copy");
       auto fromPointerValue = builder.create<fir::LoadOp>(loc, fromCoor);
       auto castTo = builder.createConvert(loc, fieldEleTy, fromPointerValue);
       builder.create<fir::StoreOp>(loc, castTo, toCoor);
@@ -1201,8 +1202,8 @@
   // Box operands may be polymorphic, it is not entirely clear from 10.2.1.3
   // if the assignment is performed on the dynamic of declared type. Use the
   // runtime assuming it is performed on the dynamic type.
-  bool hasBoxOperands = fir::getBase(lhs).getType().isa<fir::BoxType>() ||
-                        fir::getBase(rhs).getType().isa<fir::BoxType>();
+  bool hasBoxOperands = fir::getBase(lhs).getType().isa<fir::BaseBoxType>() ||
+                        fir::getBase(rhs).getType().isa<fir::BaseBoxType>();
   auto recTy = baseTy.dyn_cast<fir::RecordType>();
   assert(recTy && "must be a record type");
   if (hasBoxOperands || !recordTypeCanBeMemCopied(recTy)) {
diff --git a/flang/test/Lower/polymorphic.f90 b/flang/test/Lower/polymorphic.f90
--- a/flang/test/Lower/polymorphic.f90
+++ b/flang/test/Lower/polymorphic.f90
@@ -24,6 +24,10 @@
     procedure :: get_tmp
   end type
 
+  type p3
+    class(p3), pointer :: p(:)
+  end type
+
   contains
 
   ! Test correct access to polymorphic entity component.
@@ -182,4 +186,10 @@
 ! CHECK: %[[REBOX:.*]] = fir.rebox %[[CLASS]] : (!fir.class<!fir.ptr<!fir.array<?x!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>) -> !fir.box<!fir.array<?x!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>
 ! CHECK: fir.call @_QMpolymorphic_testPsub_with_type_array(%[[REBOX]]) {{.*}} : (!fir.box<!fir.array<?x!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>) -> ()
 
+  subroutine derived_type_assignment_with_class()
+    type(p3) :: a
+    type(p3), target :: b(10)
+    a = p3(b)
+  end subroutine
+
 end module