Two of South Korea's smaller opposition parties are coming together behind the idea of a runoff-style election to replace President Park Geun-hye.

Minor opposition Justice Party Chairwoman Sim Sang-jeung welcomed People's Party former chair Ahn Cheol-soo's proposal to introduce a runoff Friday.

Sim says it was a mistake not to include rules for a runoff in a constitutional amendment for direct presidential election carried out in 1987.

Under the current system, whichever candidate receives the most votes in a single election is awarded the presidency. 

That system is seen to favor candidates of larger political parties, whereas a runoff system would call for a second vote between the top two candidates in the event nobody receives a required number of the popular vote.