diff --git a/lib/brakeman.rb b/lib/brakeman.rb
index cd7bd2e46a1fa7d9ce33f78bb3b052bfad3e774f..4cc81f5c115c357cfcfae81b2e831678c040bf95 100644
--- a/lib/brakeman.rb
+++ b/lib/brakeman.rb
@@ -296,7 +296,7 @@ module Brakeman
   def self.write_report_to_files tracker, output_files
     output_files.each_with_index do |output_file, idx|
       File.open output_file, "w" do |f|
-        f.write tracker.report.format(output_file)
+        f.write tracker.report.format(tracker.options[:output_formats][idx])
       end
       notify "Report saved in '#{output_file}'"
     end
diff --git a/lib/brakeman/report.rb b/lib/brakeman/report.rb
index 4bd7c00bda53d18927407595d4f9ce39bbe2f63a..d9ea75246e42d73c7d680daf65e2ef052c98e656 100644
--- a/lib/brakeman/report.rb
+++ b/lib/brakeman/report.rb
@@ -283,23 +283,14 @@ class Brakeman::Report
     end
   end
 
-  # format output from filename or format
-  def format(filename_or_format)
-    case filename_or_format
-    when /\.html/, :to_html
-      to_html
-    when /\.pdf/, :to_pdf
-      to_pdf
-    when /\.csv/, :to_csv
-      to_csv
-    when /\.json/, :to_json
-      to_json
-    when /\.tabs/, :to_tabs
-      to_tabs
-    when :to_test
-      to_test
+  # format output
+  def format format
+    valid_formats = [:to_html, :to_pdf, :to_csv, :to_json, :to_tabs, :to_test, :to_s]
+
+    if valid_formats.include? format
+      self.send(format)
     else
-      to_s
+      raise "Invalid format: #{format}. Should be one of #{valid_formats.inspect}"
     end
   end
   
diff --git a/test/tests/report_generation.rb b/test/tests/report_generation.rb
index c750a7a16ccf0a195accffa7ae6aac149f015bb5..9c102f79f2cb7ebdfcd45c1de10641c55928f8c3 100644
--- a/test/tests/report_generation.rb
+++ b/test/tests/report_generation.rb
@@ -39,4 +39,10 @@ class TestReportGeneration < Test::Unit::TestCase
 
     assert report.is_a? String
   end
+
+  def test_bad_format_type
+    assert_raises RuntimeError do
+      Report.format(:to_something_else)
+    end
+  end
 end