diff --git a/configure.ac b/configure.ac
index a15733f19..073141d7a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -136,7 +136,7 @@ AC_SEARCH_LIBS([gethostbyname], [nsl])
 
 AC_CHECK_FUNCS(pipe2 accept4 eventfd)
 
-AC_CHECK_FUNCS(strndup)
+AC_CHECK_FUNCS(strnlen strndup)
 
 AC_SEARCH_LIBS([exp], [m],,
 	[AC_MSG_ERROR([exp() not found])])
diff --git a/src/string_util.c b/src/string_util.c
index b76b257ba..5d9feccf9 100644
--- a/src/string_util.c
+++ b/src/string_util.c
@@ -48,6 +48,21 @@ string_array_contains(const char *const* haystack, const char *needle)
 	return false;
 }
 
+#ifndef HAVE_STRNLEN
+
+size_t
+strnlen(const char *s, size_t max)
+{
+	assert(s != NULL);
+
+	const char *t = memchr(s, 0, max);
+	return t != NULL
+		? (size_t)(t - s)
+		: max;
+}
+
+#endif
+
 #if !defined(HAVE_STRNDUP)
 
 char *
diff --git a/src/string_util.h b/src/string_util.h
index 374fd0f91..62de53873 100644
--- a/src/string_util.h
+++ b/src/string_util.h
@@ -83,6 +83,14 @@ strchug_fast(char *p)
 bool
 string_array_contains(const char *const* haystack, const char *needle);
 
+#ifndef HAVE_STRNLEN
+
+gcc_pure
+size_t
+strnlen(const char *s, size_t max);
+
+#endif
+
 #if !defined(HAVE_STRNDUP)
 
 /**