diff --git a/lib/server_timing/timing_metric.rb b/lib/server_timing/timing_metric.rb
index ecfd045..2b07935 100644
--- a/lib/server_timing/timing_metric.rb
+++ b/lib/server_timing/timing_metric.rb
@@ -18,12 +18,17 @@ def initialize(name,duration, description: nil)
     end
 
     def to_header
-      "#{name}; dur=#{duration.to_d.truncate(2).to_f}; #{description_to_header}"
+      "#{name}=#{duration.to_d.truncate(2).to_f} #{description_to_header}"
     end
 
+    # For description the "quoted string" must be using double quotes
+    # as specified in
+    # https://www.w3.org/TR/server-timing/#the-server-timing-header-field
+    #
+    # Also semicolon should only be added if is additional filed to add
     def description_to_header
       return unless description
-      "desc='#{description}';"
+      "; \"#{description}\""
     end
   end
-end
\ No newline at end of file
+end