diff --git a/lib/Makefile.am b/lib/Makefile.am
index d709345986..8a967ca9c8 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -115,6 +115,8 @@ libshadow_la_SOURCES = \
 	lockpw.c \
 	loginprompt.c \
 	mail.c \
+	memory/strnlen/strnlen.c \
+	memory/strnlen/strnlen.h \
 	motd.c \
 	myname.c \
 	nss.c \
diff --git a/lib/memory/strnlen/strnlen.c b/lib/memory/strnlen/strnlen.c
new file mode 100644
index 0000000000..d8f60c3c96
--- /dev/null
+++ b/lib/memory/strnlen/strnlen.c
@@ -0,0 +1,7 @@
+// SPDX-FileCopyrightText: 2025-2026, Alejandro Colomar <alx@kernel.org>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#include "config.h"
+
+#include "memory/strnlen/strnlen.h"
diff --git a/lib/memory/strnlen/strnlen.h b/lib/memory/strnlen/strnlen.h
new file mode 100644
index 0000000000..4d16c8a604
--- /dev/null
+++ b/lib/memory/strnlen/strnlen.h
@@ -0,0 +1,20 @@
+// SPDX-FileCopyrightText: 2025-2026, Alejandro Colomar <alx@kernel.org>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#ifndef SHADOW_INCLUDE_LIB_MEMORY_STRNLEN_STRNLEN_H_
+#define SHADOW_INCLUDE_LIB_MEMORY_STRNLEN_STRNLEN_H_
+
+
+#include "config.h"
+
+#include <memory.h>
+
+#include "sizeof.h"
+
+
+// strnlen_a - nonstring length array
+#define strnlen_a(strn)  strnlen(strn, countof(strn))
+
+
+#endif  // include guard
diff --git a/lib/string/README b/lib/string/README
index 70274d71de..21818078cb 100644
--- a/lib/string/README
+++ b/lib/string/README
@@ -288,6 +288,11 @@ strsep/ - String separation
 	Variant of strsep2ls() that allocates the array of strings.
 	(But the strings themselves are not duplicated.)
 
+strnlen/ - String length
+
+    strnlen_a()
+	Like strnlen(3), but take an array.
+
 strftime.h
     strftime_a()
 	Like strftime(3), but takes an array.
diff --git a/lib/utmp.c b/lib/utmp.c
index 62002768e6..439c1b7293 100644
--- a/lib/utmp.c
+++ b/lib/utmp.c
@@ -30,6 +30,7 @@
 #include "alloc/malloc.h"
 #include "attr.h"
 #include "io/syslog.h"
+#include "memory/strnlen/strnlen.h"
 #include "sizeof.h"
 #include "string/strchr/strnul.h"
 #include "string/strcmp/streq.h"
@@ -301,8 +302,7 @@ prepare_utmp(const char *name, const char *line, const char *host,
 		strncpy_a(utent->ut_host, hostname);
 #endif
 #if defined(HAVE_STRUCT_UTMPX_UT_SYSLEN)
-		utent->ut_syslen = MIN(strlen(hostname),
-		                       sizeof(utent->ut_host));
+		utent->ut_syslen = strnlen_a(utent->ut_host);
 #endif
 #if defined(HAVE_STRUCT_UTMPX_UT_ADDR) || defined(HAVE_STRUCT_UTMPX_UT_ADDR_V6)
 		if (getaddrinfo (hostname, NULL, NULL, &info) == 0) {