diff --git a/test/net/addr/subnet.cpp b/test/net/addr/subnet.cpp
index 31bad90..8973bdb 100644
--- a/test/net/addr/subnet.cpp
+++ b/test/net/addr/subnet.cpp
@@ -2,6 +2,7 @@
 
 #include <stdplus/net/addr/subnet.hpp>
 
+#include <format>
 #include <string_view>
 
 #include <gtest/gtest.h>
@@ -74,6 +75,8 @@
     EXPECT_EQ("255.0.255.255/28", tsh(Subnet4(In4Addr{255, 0, 255, 255}, 28)));
     EXPECT_EQ("a 1.2.3.4/32 b",
               fmt::format("a {} b", Subnet4(In4Addr{1, 2, 3, 4}, 32)));
+    EXPECT_EQ("a 1.2.3.4/32 b",
+              std::format("a {} b", Subnet4(In4Addr{1, 2, 3, 4}, 32)));
 }
 
 TEST(Subnet6, Basic)
@@ -146,6 +149,8 @@
     EXPECT_EQ("ff00::/128", tsh(Subnet6(In6Addr{0xff}, 128)));
     EXPECT_EQ("a 102:304::/32 b",
               fmt::format("a {} b", Subnet6(In6Addr{1, 2, 3, 4}, 32)));
+    EXPECT_EQ("a 102:304::/32 b",
+              std::format("a {} b", Subnet6(In6Addr{1, 2, 3, 4}, 32)));
 }
 
 TEST(SubnetAny, Basic)
@@ -224,8 +229,12 @@
     EXPECT_EQ("ff00::/128", tsh(SubnetAny(In6Addr{0xff}, 128)));
     EXPECT_EQ("a 102:304::/32 b",
               fmt::format("a {} b", SubnetAny(In6Addr{1, 2, 3, 4}, 32)));
+    EXPECT_EQ("a 102:304::/32 b",
+              std::format("a {} b", SubnetAny(In6Addr{1, 2, 3, 4}, 32)));
     EXPECT_EQ("a 1.2.3.4/32 b",
               fmt::format("a {} b", SubnetAny(In4Addr{1, 2, 3, 4}, 32)));
+    EXPECT_EQ("a 1.2.3.4/32 b",
+              std::format("a {} b", SubnetAny(In4Addr{1, 2, 3, 4}, 32)));
 }
 
 TEST(Ops, MaskToPfx)