diff --git a/config.h.in b/config.h.in
index 81bd41e2..bd44ead2 100644
--- a/config.h.in
+++ b/config.h.in
@@ -55,6 +55,9 @@
 /* Define to 1 if you have the <string.h> header file. */
 #undef HAVE_STRING_H
 
+/* Define to 1 if you have the `strnlen' function. */
+#undef HAVE_STRNLEN
+
 /* Define to 1 if you have the `strrchr' function. */
 #undef HAVE_STRRCHR
 
diff --git a/configure.in b/configure.in
index 719acbe7..8c2eea6d 100644
--- a/configure.in
+++ b/configure.in
@@ -44,7 +44,7 @@ AC_TYPE_SSIZE_T
 
 # Checks for library functions.
 AC_FUNC_MALLOC
-AC_CHECK_FUNCS([memset select socket strcasecmp strrchr getaddrinfo])
+AC_CHECK_FUNCS([memset select socket strcasecmp strrchr getaddrinfo strnlen])
 
 AC_CONFIG_HEADERS([config.h])