diff --git a/flang/include/flang/Optimizer/Builder/FIRBuilder.h b/flang/include/flang/Optimizer/Builder/FIRBuilder.h
--- a/flang/include/flang/Optimizer/Builder/FIRBuilder.h
+++ b/flang/include/flang/Optimizer/Builder/FIRBuilder.h
@@ -336,7 +336,7 @@
   /// Array entities are boxed with a shape and possibly a shift. Character
   /// entities are boxed with a LEN parameter.
   mlir::Value createBox(mlir::Location loc, const fir::ExtendedValue &exv,
-                        bool isPolymorphic = false);
+                        bool isPolymorphic = false, bool isAssumedType = false);
 
   mlir::Value createBox(mlir::Location loc, mlir::Type boxType,
                         mlir::Value addr, mlir::Value shape, mlir::Value slice,
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
@@ -2714,12 +2714,13 @@
             // actually a variable.
             box = Fortran::evaluate::IsVariable(*expr)
                       ? builder.createBox(loc, genBoxArg(*expr),
-                                          fir::isPolymorphicType(argTy))
+                                          fir::isPolymorphicType(argTy),
+                                          fir::isBoxNone(argTy))
                       : builder.createBox(getLoc(), genTempExtAddr(*expr),
-                                          fir::isPolymorphicType(argTy));
-
+                                          fir::isPolymorphicType(argTy),
+                                          fir::isBoxNone(argTy));
             if (box.getType().isa<fir::BoxType>() &&
-                fir::isPolymorphicType(argTy)) {
+                fir::isPolymorphicType(argTy) && !fir::isBoxNone(argTy)) {
               mlir::Type actualTy = argTy;
               if (Fortran::lower::isParentComponent(*expr))
                 actualTy = fir::BoxType::get(converter.genType(*expr));
@@ -2758,7 +2759,6 @@
               box = fir::getBase(newExv);
             }
           }
-
           caller.placeInput(arg, box);
         }
       } else if (arg.passBy == PassBy::AddressAndLength) {
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
@@ -506,7 +506,8 @@
 
 mlir::Value fir::FirOpBuilder::createBox(mlir::Location loc,
                                          const fir::ExtendedValue &exv,
-                                         bool isPolymorphic) {
+                                         bool isPolymorphic,
+                                         bool isAssumedType) {
   mlir::Value itemAddr = fir::getBase(exv);
   if (itemAddr.getType().isa<fir::BaseBoxType>())
     return itemAddr;
@@ -525,7 +526,10 @@
     boxTy = fir::BoxType::get(elementType);
     if (isPolymorphic) {
       elementType = fir::updateTypeForUnlimitedPolymorphic(elementType);
-      boxTy = fir::ClassType::get(elementType);
+      if (isAssumedType)
+        boxTy = fir::BoxType::get(elementType);
+      else
+        boxTy = fir::ClassType::get(elementType);
     }
   }