Japanese superlong government bonds drew a record foreign inflow last month as heightened risk aversion amid U.S. tariff policy burnished the securities’ allure as a haven.

Global funds bought a net ¥2.18 trillion ($15.5 billion) of the nation’s debt with original maturities of more than 10 years, according to the latest data from Japan Securities Dealers Association released on Monday. Net purchases across all tenors totaled ¥6.03 trillion, the second highest on record dating back to 2004.

Demand for Japanese debt has risen since March as the Trump administration’s higher tariffs sparked a surge in market volatility. Separate preliminary weekly data from the Finance Ministry indicate that foreign inflows remained elevated in the nation’s debt market this month.

In contrast, local insurance companies sold a record ¥645.8 billion of super-long bonds in March. Thirty-year yields rose to the highest since 2006 in mid-March before climbing further this month, according to Bloomberg-compiled data, as the Bank of Japan slowed purchases of super-long debt and surging volatility in U.S. Treasuries roiled the global debt market.

"The scarcity of buyers and the rise in long-term and long-end U.S. interest rates likely discouraged active investment” in Japan’s superlong bonds, Shoki Omori, chief desk strategist at Mizuho Securities, wrote in a note. "March coincides with the Japanese fiscal year-end, during which investors typically adjust their balance sheets.”

Taiju Life Insurance said last week that while 30- and 40-year yields are attractive, the market has not yet stabilized. In the fiscal year that started in April, Daido Life Insurance plans to increase its holdings of domestic bonds by roughly the same amount as the previous fiscal year, while Fukoku Mutual Life Insurance plans to invest in super-long government bonds.