diff --git a/src/goto-programs/class_identifier.cpp b/src/goto-programs/class_identifier.cpp
index bc4997df852..ace0626e317 100644
--- a/src/goto-programs/class_identifier.cpp
+++ b/src/goto-programs/class_identifier.cpp
@@ -30,7 +30,7 @@ static exprt build_class_identifier(
     const typet &type=ns.follow(e.type());
     const struct_typet &struct_type=to_struct_type(type);
     const struct_typet::componentst &components=struct_type.components();
-    assert(!components.empty());
+    INVARIANT(!components.empty(), "class structs cannot be empty");
 
     const auto &first_member_name=components.front().get_name();
     member_exprt member_expr(
@@ -61,10 +61,9 @@ exprt get_class_identifier_field(
   // Get a pointer from which we can extract a clsid.
   // If it's already a pointer to an object of some sort, just use it;
   // if it's void* then use the suggested type.
+  PRECONDITION(this_expr_in.type().id() == ID_pointer);
 
   exprt this_expr=this_expr_in;
-  assert(this_expr.type().id()==ID_pointer &&
-         "Non-pointer this-arg in remove-virtuals?");
   const auto &points_to=this_expr.type().subtype();
   if(points_to==empty_typet())
     this_expr=typecast_exprt(this_expr, pointer_type(suggested_type));
diff --git a/src/goto-programs/compute_called_functions.cpp b/src/goto-programs/compute_called_functions.cpp
index 6592f603537..9c597760a43 100644
--- a/src/goto-programs/compute_called_functions.cpp
+++ b/src/goto-programs/compute_called_functions.cpp
@@ -21,14 +21,18 @@ void compute_address_taken_functions(
   forall_operands(it, src)
     compute_address_taken_functions(*it, address_taken);
 
-  if(src.id()==ID_address_of &&
-     src.type().id()==ID_pointer &&
-     src.type().subtype().id()==ID_code)
+  if(src.id() == ID_address_of)
   {
-    assert(src.operands().size()==1);
-    const exprt &op=src.op0();
-    if(op.id()==ID_symbol)
-      address_taken.insert(to_symbol_expr(op).get_identifier());
+    const address_of_exprt &address = to_address_of_expr(src);
+
+    if(
+      address.type().id() == ID_pointer &&
+      address.type().subtype().id() == ID_code)
+    {
+      const exprt &target = address.object();
+      if(target.id() == ID_symbol)
+        address_taken.insert(to_symbol_expr(target).get_identifier());
+    }
   }
 }