diff --git a/lib/polo/adapters/mysql.rb b/lib/polo/adapters/mysql.rb
index 11a3486..6562b51 100644
--- a/lib/polo/adapters/mysql.rb
+++ b/lib/polo/adapters/mysql.rb
@@ -4,7 +4,7 @@ class MySQL
       def on_duplicate_key_update(inserts, records)
         insert_and_record = inserts.zip(records)
         insert_and_record.map do |insert, record|
-          attrs = record.is_a?(Hash) ? record.fetch(:values) : record.attributes
+          attrs = record.is_a?(Hash) ? record.fetch(:values) : record.attributes.slice(*record.class.column_names)
           values_syntax = attrs.keys.map do |key|
             "`#{key}` = VALUES(`#{key}`)"
           end
@@ -22,4 +22,4 @@ def ignore_transform(inserts, records)
       end
     end
   end
-end
\ No newline at end of file
+end
diff --git a/lib/polo/adapters/postgres.rb b/lib/polo/adapters/postgres.rb
index 6bd1c37..e6e5c47 100644
--- a/lib/polo/adapters/postgres.rb
+++ b/lib/polo/adapters/postgres.rb
@@ -1,11 +1,59 @@
 module Polo
   module Adapters
     class Postgres
-      # TODO: Implement UPSERT. This command became available in 9.1.
-      #
-      # See: http://www.the-art-of-web.com/sql/upsert/
       def on_duplicate_key_update(inserts, records)
-        raise 'on_duplicate: :override is not currently supported in the PostgreSQL adapter'
+        @pg_version ||= ActiveRecord::Base.connection.select_value('SELECT version()')[/PostgreSQL ([\d\.]+)/, 1]
+
+        insert_and_record = inserts.zip(records)
+        insert_and_record.map do |insert, record|
+          if @pg_version < '9.5.0'
+            naive_update_insert(insert, record)
+          else
+            add_upsert_to_insert(insert, record)
+          end
+        end
+      end
+
+      def add_upsert_to_insert(insert, record)
+        if record.is_a?(Hash)
+          return naive_update_insert(insert, record)
+        end
+
+        attrs = record.is_a?(Hash) ? record.fetch(:values) : record.attributes.slice(*record.class.column_names)
+        values_syntax = attrs.keys.reject { |key| key.to_s == 'id' }.map do |key|
+          %{"#{key}" = EXCLUDED."#{key}"}
+        end
+
+        # Conflict on id column
+        on_dup_syntax = "ON CONFLICT (#{record.class.primary_key}) DO UPDATE SET #{values_syntax.join(', ')}"
+
+        "#{insert} #{on_dup_syntax}"
+      end
+
+      def naive_update_insert(insert, record)
+        table_name, id = table_name_and_key_for(record)
+
+        attrs = record.is_a?(Hash) ? record.fetch(:values) : record.attributes_before_type_cast.slice(*record.class.column_names)
+        updates = attrs.except('id').map do |key, value|
+          column = ActiveRecord::Base.connection.send(:quote_column_name, key)
+
+          ActiveRecord::Base.send(:sanitize_sql_array, ["#{column} = ?", value])
+        end
+        condition = if id.blank?
+                      record[:values].map { |k, v|
+                        column = ActiveRecord::Base.connection.send(:quote_column_name, k)
+                        ActiveRecord::Base.send(:sanitize_sql_array, ["#{column} = ?", v])
+                      }.join(' and ')
+                    else
+                      "id = #{id}"
+                    end
+
+        "do $$
+          begin
+            #{insert};
+            exception when unique_violation then
+            update #{table_name} set #{updates.join(', ')} where #{condition};
+            end $$;"
       end
 
       # Internal: Transforms an INSERT with PostgreSQL-specific syntax. Ignores
@@ -21,17 +69,22 @@ def on_duplicate_key_update(inserts, records)
       def ignore_transform(inserts, records)
         insert_and_record = inserts.zip(records)
         insert_and_record.map do |insert, record|
-          if record.is_a?(Hash)
-            id = record.fetch(:values)[:id]
-            table_name = record.fetch(:table_name)
-          else
-            id = record[:id]
-            table_name = record.class.arel_table.name
-          end
+          table_name, id = table_name_and_key_for(record)
           insert = insert.gsub(/VALUES \((.+)\)$/m, 'SELECT \\1')
           insert << " WHERE NOT EXISTS (SELECT 1 FROM #{table_name} WHERE id=#{id});"
         end
       end
+
+      def table_name_and_key_for(record)
+        if record.is_a?(Hash)
+          id = record.fetch(:values)[:id]
+          table_name = record.fetch(:table_name)
+        else
+          id = record[:id]
+          table_name = record.class.arel_table.name
+        end
+        [table_name, id]
+      end
     end
   end
 end