diff --git a/kit/mcpp.toml b/kit/mcpp.toml
index 0412d1a..df896e5 100644
--- a/kit/mcpp.toml
+++ b/kit/mcpp.toml
@@ -1,7 +1,7 @@
 [package]
 namespace   = "mcpplibs"
 name        = "openkal-kit"
-version     = "0.3.0"
+version     = "0.3.1"
 description = "Facilities composed from openkal's interfaces. Not part of the specification, and structurally incapable of being mistaken for it."
 license     = "Apache-2.0"
 authors     = ["mcpplibs"]
@@ -98,4 +98,4 @@ openkal = "0.25.0"
 # same reason: a change spanning the specification and an implementation must be
 # tested against both halves as written, not against whichever half is published.
 [target.'cfg(os = "linux")'.dev-dependencies]
-openkal-linux = { version = "0.25.0", features = ["standalone"] }
+openkal-linux = { version = "0.26.0", features = ["standalone"] }
diff --git a/kit/src/endpoint.cppm b/kit/src/endpoint.cppm
index 91df6a1..365c32c 100644
--- a/kit/src/endpoint.cppm
+++ b/kit/src/endpoint.cppm
@@ -104,10 +104,13 @@ constexpr format_result format_v4(const kal_endpoint& ep, char* out, kal_uintptr
     if (cap < 22) return { 0, false };
 
     kal_uintptr n = 0;
+    // EVERY DIGIT OF THE NUMBER (0.3.1). An octet has at most three and a port
+    // five; written as three, port 8080 came out as "080".
     auto digits = [&](unsigned v) {
-        if (v >= 100) out[n++] = static_cast<char>('0' + (v / 100) % 10);
-        if (v >= 10)  out[n++] = static_cast<char>('0' + (v / 10) % 10);
-        out[n++] = static_cast<char>('0' + v % 10);
+        char reversed[5] = {};
+        int k = 0;
+        do { reversed[k++] = static_cast<char>('0' + v % 10); v /= 10; } while (v != 0 && k < 5);
+        while (k > 0) out[n++] = reversed[--k];
     };
 
     for (int octet = 0; octet < 4; ++octet) {
diff --git a/kit/tests/kit.cpp b/kit/tests/kit.cpp
index c41b390..5cc2f9c 100644
--- a/kit/tests/kit.cpp
+++ b/kit/tests/kit.cpp
@@ -71,6 +71,27 @@ void endpoint_section() {
               std::memcmp(again.ep.addr, ep.addr, 4) == 0,
               "formatting and parsing are inverses");
     }
+    // EVERY DIGIT OF A PORT (0.3.1). The formatter wrote at most three digits
+    // of each number, which is every digit of an octet and not of a port:
+    // 8080 came out as "080". No port is written as none, and each other one
+    // is written whole and reads back as itself.
+    {
+        struct { kal_u32 port; const char* text; } const ports[] = {
+            { 0,     "127.0.0.1" },
+            { 80,    "127.0.0.1:80" },
+            { 8080,  "127.0.0.1:8080" },
+            { 65535, "127.0.0.1:65535" },
+        };
+        for (const auto& p : ports) {
+            char buf[32] = {};
+            const auto f = format_v4(loopback_v4(p.port), buf, sizeof buf);
+            const kal_uintptr len = std::strlen(p.text);
+            check(f.ok && f.n == len && std::memcmp(buf, p.text, len) == 0,
+                  "a port is written with all its digits");
+            const auto again = parse_v4(buf, f.n);
+            check(again.ok && again.ep.port == p.port, "and reads back as the port it was");
+        }
+    }
     {
         char small[8] = {};
         const auto f = format_v4(loopback_v4(443), small, sizeof small);