diff --git a/app/models/error_report.rb b/app/models/error_report.rb
index 365cc3b..2e29b01 100644
--- a/app/models/error_report.rb
+++ b/app/models/error_report.rb
@@ -59,7 +59,7 @@ class ErrorReport
   private
   def fingerprint_source
     {
-      :backtrace => backtrace.lines[0..3],
+      :backtrace => backtrace_head.map(&:to_s),
       :error_class => error_class,
       :component => component,
       :action => action,
@@ -68,5 +68,9 @@ class ErrorReport
     }
   end
 
+  def backtrace_head
+    backtrace.lines[0..3]
+  end
+
 end
 
--
libgit2 0.21.2