Taken from: https://groups.google.com/g/linux.debian.bugs.dist/c/mX4GpUJih4k.

--- a/configure.ac
+++ b/configure.ac
@@ -132,6 +132,16 @@ if test "$os_unix" = "yes"; then
 	AC_CHECK_FUNCS([getpeereid])
 	AC_CHECK_FUNCS([getpeerucred])
 	AC_CHECK_FUNCS([issetugid])
+	case "$host_os" in
+	kfreebsd*-gnu | gnu*)
+		have_getpeereid=no
+		AC_CHECK_LIB(bsd, getpeereid, have_getpeereid=yes)
+		if test "x$have_getpeereid" = "xyes"; then
+			AC_DEFINE([HAVE_GETPEEREID], [1], [have getpeereid])
+			AC_SEARCH_LIBS([getpeereid], [bsd])
+		fi
+	;;
+	esac
 
 	AC_CACHE_CHECK([for thread-local storage class],
 		[ac_cv_tls_keyword],

--- a/common/unix-peer.c
+++ b/common/unix-peer.c
@@ -47,6 +47,11 @@
 #  include <ucred.h>
 #endif
 
+#ifdef HAVE_GETPEEREID
+/* Declare getpeereid from /usr/include/bsd/unistd.h */
+extern int getpeereid(int s, uid_t *euid, gid_t *egid);
+#endif
+
 /* Returns the unix domain socket peer information.
  * Returns zero on success.
  */
@@ -73,7 +78,8 @@ p11_get_upeer_id (int cfd, uid_t *uid, u
 		*pid = cr.pid;
 
 #elif defined(HAVE_GETPEEREID)
-	/* *BSD/MacOSX */
+	/* *BSD/MacOSX/kFreeBSD/Hurd */
+
 	uid_t euid;
 	gid_t egid;
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