diff --git a/test/net/addr/ether.cpp b/test/net/addr/ether.cpp
index bff7248..cf23223 100644
--- a/test/net/addr/ether.cpp
+++ b/test/net/addr/ether.cpp
@@ -2,6 +2,8 @@
 
 #include <stdplus/net/addr/ether.hpp>
 
+#include <format>
+
 #include <gtest/gtest.h>
 
 namespace stdplus
@@ -44,6 +46,9 @@
     EXPECT_EQ(
         "a 01:02:03:04:05:67 b",
         fmt::format("a {} b", EtherAddr{0x01, 0x02, 0x03, 0x04, 0x05, 0x67}));
+    EXPECT_EQ(
+        "a 01:02:03:04:05:67 b",
+        std::format("a {} b", EtherAddr{0x01, 0x02, 0x03, 0x04, 0x05, 0x67}));
 }
 
 TEST(FromStr, EtherAddr)
diff --git a/test/net/addr/ip.cpp b/test/net/addr/ip.cpp
index 2ce2580..5fef26a 100644
--- a/test/net/addr/ip.cpp
+++ b/test/net/addr/ip.cpp
@@ -3,6 +3,7 @@
 #include <stdplus/net/addr/ip.hpp>
 #include <stdplus/numeric/endian.hpp>
 
+#include <format>
 #include <string_view>
 
 #include <gtest/gtest.h>
@@ -48,6 +49,7 @@
     EXPECT_EQ("1.15.3.4", tsh(In4Addr{1, 15, 3, 4}));
     EXPECT_EQ("0.0.0.0", tsh(In4Addr{}));
     EXPECT_EQ("a 1.15.3.4 b", fmt::format("a {} b", In4Addr{1, 15, 3, 4}));
+    EXPECT_EQ("a 1.15.3.4 b", std::format("a {} b", In4Addr{1, 15, 3, 4}));
 }
 
 TEST(EqualOperator, In6Addr)
@@ -157,6 +159,7 @@
                                                 0xff, 0xff, 192, 168, 0, 1}));
 
     EXPECT_EQ("a ff00:: b", fmt::format("a {} b", In6Addr{0xff}));
+    EXPECT_EQ("a ff00:: b", std::format("a {} b", In6Addr{0xff}));
 }
 
 TEST(EqualOperator, InAnyAddr)
@@ -221,6 +224,7 @@
     EXPECT_EQ("ff::", tsh(In6Addr{0, 0xff}));
 
     EXPECT_EQ("a ff00:: b", fmt::format("a {} b", InAnyAddr{In6Addr{0xff}}));
+    EXPECT_EQ("a ff00:: b", std::format("a {} b", InAnyAddr{In6Addr{0xff}}));
     EXPECT_NE("0.0.0.0"_ip, std::optional<InAnyAddr>());
     EXPECT_EQ("0.0.0.0"_ip, std::optional<InAnyAddr>(In4Addr{}));
 }
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)