diff --git a/flang/lib/Lower/CallInterface.cpp b/flang/lib/Lower/CallInterface.cpp
--- a/flang/lib/Lower/CallInterface.cpp
+++ b/flang/lib/Lower/CallInterface.cpp
@@ -965,7 +965,14 @@
     mlir::Type boxType = fir::wrapInClassOrBoxType(
         type, obj.type.type().IsPolymorphic(), obj.type.type().IsAssumedType());
 
-    if (obj.attrs.test(Attrs::Allocatable) || obj.attrs.test(Attrs::Pointer)) {
+    if (obj.type.type().IsAssumedType() && isBindC) {
+      mlir::Type voidPtrType = fir::ReferenceType::get(
+          mlir::NoneType::get(&interface.converter.getMLIRContext()));
+      addFirOperand(voidPtrType, nextPassedArgPosition(), Property::BaseAddress,
+                    attrs);
+      addPassedArg(PassEntityBy::BaseAddress, entity, characteristics);
+    } else if (obj.attrs.test(Attrs::Allocatable) ||
+               obj.attrs.test(Attrs::Pointer)) {
       // Pass as fir.ref<fir.box> or fir.ref<fir.class>
       mlir::Type boxRefType = fir::ReferenceType::get(boxType);
       addFirOperand(boxRefType, nextPassedArgPosition(), Property::MutableBox,
diff --git a/flang/test/Lower/polymorphic-types.f90 b/flang/test/Lower/polymorphic-types.f90
--- a/flang/test/Lower/polymorphic-types.f90
+++ b/flang/test/Lower/polymorphic-types.f90
@@ -172,13 +172,13 @@
   end subroutine assumed_type_dummy
 
   ! CHECK-LABEL: func.func @assumed_type_dummy(
-  ! CHECK-SAME: %{{.*}}: !fir.box<none>
+  ! CHECK-SAME: %{{.*}}: !fir.ref<none>
 
   subroutine assumed_type_dummy_array(a) bind(c)
     type(*) :: a(:)
   end subroutine assumed_type_dummy_array
 
   ! CHECK-LABEL: func.func @assumed_type_dummy_array(
-  ! CHECK-SAME: %{{.*}}: !fir.box<!fir.array<?xnone>>
+  ! CHECK-SAME: %{{.*}}: !fir.ref<none>
 
 end module