diff --git a/flang/lib/Lower/ConvertExpr.cpp b/flang/lib/Lower/ConvertExpr.cpp
--- a/flang/lib/Lower/ConvertExpr.cpp
+++ b/flang/lib/Lower/ConvertExpr.cpp
@@ -4307,7 +4307,7 @@
   llvm::SmallVector<mlir::Value> getShape(ArrayOperand array) {
     if (array.slice)
       return computeSliceShape(array.slice);
-    if (array.memref.getType().isa<fir::BoxType>())
+    if (array.memref.getType().isa<fir::BaseBoxType>())
       return fir::factory::readExtents(builder, getLoc(),
                                        fir::BoxValue{array.memref});
     return fir::factory::getExtents(array.shape);
diff --git a/flang/lib/Optimizer/CodeGen/CGOps.cpp b/flang/lib/Optimizer/CodeGen/CGOps.cpp
--- a/flang/lib/Optimizer/CodeGen/CGOps.cpp
+++ b/flang/lib/Optimizer/CodeGen/CGOps.cpp
@@ -56,7 +56,7 @@
 
 unsigned fir::cg::XArrayCoorOp::getRank() {
   auto memrefTy = getMemref().getType();
-  if (memrefTy.isa<fir::BoxType>())
+  if (memrefTy.isa<fir::BaseBoxType>())
     if (auto seqty =
             fir::dyn_cast_ptrOrBoxEleTy(memrefTy).dyn_cast<fir::SequenceType>())
       return seqty.getDimension();
diff --git a/flang/lib/Optimizer/CodeGen/CodeGen.cpp b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
--- a/flang/lib/Optimizer/CodeGen/CodeGen.cpp
+++ b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
@@ -2293,7 +2293,7 @@
     mlir::Value offset = genConstantIndex(loc, idxTy, rewriter, 0);
     const bool isShifted = !coor.getShift().empty();
     const bool isSliced = !coor.getSlice().empty();
-    const bool baseIsBoxed = coor.getMemref().getType().isa<fir::BoxType>();
+    const bool baseIsBoxed = coor.getMemref().getType().isa<fir::BaseBoxType>();
 
     // For each dimension of the array, generate the offset calculation.
     for (unsigned i = 0; i < rank; ++i, ++indexOffset, ++shapeOffset,
diff --git a/flang/lib/Optimizer/Dialect/FIROps.cpp b/flang/lib/Optimizer/Dialect/FIROps.cpp
--- a/flang/lib/Optimizer/Dialect/FIROps.cpp
+++ b/flang/lib/Optimizer/Dialect/FIROps.cpp
@@ -380,7 +380,7 @@
     } else {
       auto s = shapeTy.cast<fir::ShiftType>();
       shapeTyRank = s.getRank();
-      if (!getMemref().getType().isa<fir::BoxType>())
+      if (!getMemref().getType().isa<fir::BaseBoxType>())
         return emitOpError("shift can only be provided with fir.box memref");
     }
     if (arrDim && arrDim != shapeTyRank)
@@ -449,7 +449,7 @@
     } else {
       auto s = shapeTy.cast<fir::ShiftType>();
       shapeTyRank = s.getRank();
-      if (!getMemref().getType().isa<fir::BoxType>())
+      if (!getMemref().getType().isa<fir::BaseBoxType>())
         return emitOpError("shift can only be provided with fir.box memref");
     }
     if (arrDim && arrDim != shapeTyRank)
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
@@ -76,4 +76,18 @@
 ! CHECK: %[[CALL_RES:.*]] = fir.call @_QMpolymorphic_testPtest_fct_ret_class() {{.*}}: () -> !fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>
 ! CHECK: fir.save_result %[[CALL_RES]] to %[[RESULT]] : !fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>, !fir.ref<!fir.class<!fir.ptr<!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>
 
+  subroutine implicit_loop_with_polymorphic()
+    class(p1), allocatable :: p(:)
+    allocate(p(3))
+    p%a = [ 1, 2, 3 ]
+  end subroutine
+
+! CHECK-LABEL: func.func @_QMpolymorphic_testPimplicit_loop_with_polymorphic() {
+! CHECK: %{{.*}} = fir.array_load %{{.*}}(%{{.*}}) [%{{.*}}] : (!fir.class<!fir.heap<!fir.array<?x!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>, !fir.shift<1>, !fir.slice<1>) -> !fir.array<?xi32>
+! CHECK: %{{.*}} = fir.do_loop %{{.*}} = %{{.*}} to %{{.*}} step %{{.*}} unordered iter_args(%{{.*}} = %{{.*}}) -> (!fir.array<?xi32>) {
+! CHECK: %{{.*}} = fir.array_fetch %{{.*}}, %{{.*}} : (!fir.array<3xi32>, index) -> i32
+! CHECK: %{{.*}} = fir.array_update %{{.*}}, %{{.*}}, %{{.*}} : (!fir.array<?xi32>, i32, index) -> !fir.array<?xi32>
+! CHECK: }
+! CHECK: fir.array_merge_store %{{.*}}, %{{.*}} to %{{.*}}[%{{.*}}] : !fir.array<?xi32>, !fir.array<?xi32>, !fir.class<!fir.heap<!fir.array<?x!fir.type<_QMpolymorphic_testTp1{a:i32,b:i32}>>>>, !fir.slice<1>
+
 end module