diff --git a/lib/instapaper/bookmark.rb b/lib/instapaper/bookmark.rb
index 1e5c432..f9c07f6 100644
--- a/lib/instapaper/bookmark.rb
+++ b/lib/instapaper/bookmark.rb
@@ -13,8 +13,8 @@ module Instapaper
     attribute? :description, Types::String
     attribute? :instapaper_hash, Types::String
     attribute? :private_source, Types::String
-    attribute? :progress_timestamp, Types::Integer.optional
-    attribute? :time, Types::Integer.optional
+    attribute? :progress_timestamp, Types::UnixTime
+    attribute? :time, Types::UnixTime
     attribute? :progress, Types::StringOrInteger
     attribute? :starred, Types::StringOrInteger
   end
diff --git a/lib/instapaper/highlight.rb b/lib/instapaper/highlight.rb
index 2f82762..09bb1a9 100644
--- a/lib/instapaper/highlight.rb
+++ b/lib/instapaper/highlight.rb
@@ -11,6 +11,6 @@ module Instapaper
     attribute :bookmark_id, Types::Integer
     attribute :text, Types::String
     attribute :position, Types::Integer
-    attribute :time, Types::Integer.optional
+    attribute :time, Types::UnixTime
   end
 end
diff --git a/lib/instapaper/types.rb b/lib/instapaper/types.rb
index 2781b5c..ce65c4b 100644
--- a/lib/instapaper/types.rb
+++ b/lib/instapaper/types.rb
@@ -18,5 +18,17 @@ module Instapaper
         !!value
       end
     end
+
+    # Converts Unix timestamps to Time objects
+    UnixTime = Types::Time.constructor do |value|
+      case value
+      when ::Time
+        value
+      when nil
+        nil
+      else
+        ::Time.at(value.to_i)
+      end
+    end
   end
 end