diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index d392f759bd77753159aa01125361b685d9046db8..993f628fa33714908e8ee45c1cebb1b2c2d1b844 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -877,7 +877,7 @@ def where_unscoping(target_value)
           subrelation = (rel.left.kind_of?(Arel::Attributes::Attribute) ? rel.left : rel.right)
           subrelation.name == target_value
         else
-          raise "unscope(where: #{target_value.inspect}) failed: unscoping #{rel.class} is unimplemented."
+          raise "unscope(where: #{target_value.inspect}) failed: unscoping #{rel.class} \"#{rel}\" is unimplemented."
         end
       end