South Korean presidential spokesman Park Soo-hyun said in a press release, cited by the Yonhap news agency, the two leaders had "reached an agreement in principle to revise the 'missile guideline', Reuters reported.
The 1979 guideline was last amended five years ago to extend the allowed range of South Korean ballistic missiles to almost 500 miles and increase their payload to 1,100 pounds.
Park reportedly said Trump had agreed to double the weight cap to reach the maximum payload as South Korea had hoped. The White House said earlier the US president also approved planned South Korean purchases of billions of dollars in US military equipment to counter the North.