diff --git a/lib/web_console/injector.rb b/lib/web_console/injector.rb
index 1f172038..d3bb3253 100644
--- a/lib/web_console/injector.rb
+++ b/lib/web_console/injector.rb
@@ -16,7 +16,7 @@ def inject(content)
       # Set Content-Length header to the size of the current body
       # + the extra content. Otherwise the response will be truncated.
       if @headers["Content-Length"]
-        @headers["Content-Length"] = @body.bytesize + content.bytesize
+        @headers["Content-Length"] = (@body.bytesize + content.bytesize).to_s
       end
 
       [
diff --git a/test/web_console/injector_test.rb b/test/web_console/injector_test.rb
index 7628baf2..277fa976 100644
--- a/test/web_console/injector_test.rb
+++ b/test/web_console/injector_test.rb
@@ -32,7 +32,7 @@ class InjectorTest < ActiveSupport::TestCase
       body = [ "foo" ]
       headers = { "Content-Length" => 3 }
 
-      assert_equal [ [ "foobar" ], { "Content-Length" => 6 } ], Injector.new(body, headers).inject("bar")
+      assert_equal [ [ "foobar" ], { "Content-Length" => "6" } ], Injector.new(body, headers).inject("bar")
     end
   end
 end