diff --git a/lib/libc/aarch64/string/strlcat.c b/lib/libc/aarch64/string/strlcat.c
index c3c996163ade..fe2e75d091c5 100644
--- a/lib/libc/aarch64/string/strlcat.c
+++ b/lib/libc/aarch64/string/strlcat.c
@@ -1,25 +1,27 @@
 /*-
  * SPDX-License-Identifier: BSD-2-Clause
  *
  * Copyright (c) 2023 Robert Clausecker
  */
 
 #include <sys/cdefs.h>
 
 #include <string.h>
 
+#undef strlcat	/* _FORTIFY_SOURCE */
+
 void *__memchr_aarch64(const void *, int, size_t);
 size_t __strlcpy(char *restrict, const char *restrict, size_t);
 
 size_t
 strlcat(char *restrict dst, const char *restrict src, size_t dstsize)
 {
 	char *loc = __memchr_aarch64(dst, '\0', dstsize);
 
 	if (loc != NULL) {
 		size_t dstlen = (size_t)(loc - dst);
 
 		return (dstlen + __strlcpy(loc, src, dstsize - dstlen));
 	} else
 		return (dstsize + strlen(src));
 }
diff --git a/lib/libc/aarch64/string/strncat.c b/lib/libc/aarch64/string/strncat.c
index 33b278ac5e04..2c63ab50b3c3 100644
--- a/lib/libc/aarch64/string/strncat.c
+++ b/lib/libc/aarch64/string/strncat.c
@@ -1,29 +1,31 @@
 /*-
  * SPDX-License-Identifier: BSD-2-Clause
  *
  * Copyright (c) 2023 Robert Clausecker
  */
 
 #include <sys/cdefs.h>
 
 #include <string.h>
 
+#undef strncat	/* _FORTIFY_SOURCE */
+
 void *__memccpy(void *restrict, const void *restrict, int, size_t);
 
 char *
 strncat(char *dest, const char *src, size_t n)
 {
 	size_t len;
 	char *endptr;
 
 	len = strlen(dest);
 	endptr = __memccpy(dest + len, src, '\0', n);
 
 	/* avoid an extra branch */
 	if (endptr == NULL)
 		endptr = dest + len + n + 1;
 
 	endptr[-1] = '\0';
 
 	return (dest);
 }