#dup array_of_attributes a bit earlier - there's no point in duping the primary_key nulls we might put in next

lib/activerecord-import/import.rb

@@ -180,6 +180,9 @@ class ActiveRecord::Base
         raise ArgumentError.new( "Invalid arguments!" )
       end
 
+      # dup the passed in array so we don't modify it unintentionally
+      array_of_attributes = array_of_attributes.dup
+
       # Force the primary key col into the insert if it's not
       # on the list and we are using a sequence and stuff a nil
       # value for it into each row so the sequencer will fire later
@@ -188,9 +191,6 @@ class ActiveRecord::Base
          array_of_attributes.each { |a| a << nil }
       end
 
-      # dup the passed in array so we don't modify it unintentionally
-      array_of_attributes = array_of_attributes.dup
-
       # record timestamps unless disabled in ActiveRecord::Base
       if record_timestamps && options.delete( :timestamps )
          add_special_rails_stamps column_names, array_of_attributes, options