diff --git a/db/migrate/20121003223358_extract_backtraces.rb b/db/migrate/20121003223358_extract_backtraces.rb
index b6ab319..388f905 100644
--- a/db/migrate/20121003223358_extract_backtraces.rb
+++ b/db/migrate/20121003223358_extract_backtraces.rb
@@ -2,6 +2,7 @@ class ExtractBacktraces < Mongoid::Migration
   def self.up
     say "It could take long time (hours if you have many Notices)"
     Notice.unscoped.all.each do |notice|
+      next if notice.backtrace.present? || notice['backtrace'].nil?
       backtrace = Backtrace.find_or_create(:raw => notice['backtrace'] || [])
       notice.backtrace = backtrace
       notice['backtrace'] = nil
@@ -12,4 +13,4 @@ class ExtractBacktraces < Mongoid::Migration
 
   def self.down
   end
-end
+end
\ No newline at end of file
--
libgit2 0.21.2