diff -up s6-2.13.0.0/src/daemontools-extras/s6-socklog.c.orig s6-2.13.0.0/src/daemontools-extras/s6-socklog.c
--- s6-2.13.0.0/src/daemontools-extras/s6-socklog.c.orig	2024-08-08 21:45:07.257448848 +0300
+++ s6-2.13.0.0/src/daemontools-extras/s6-socklog.c	2024-08-08 21:46:02.416505236 +0300
@@ -194,7 +194,7 @@ int main (int argc, char const *const *a
             char fmt[IP46_FMT + UINT16_FMT + 3] ;
             size_t m = ip46_fmt(fmt, &ip) ;
             fmt[m++] = '_' ;
-            m += uint16_fmt(fmt, port) ;
+            m += uint16_fmt(&fmt[m], port) ;
             fmt[m++] = ':' ; fmt[m++] = ' ' ;
             buffer_putnoflush(&b1, fmt, m) ;
           }