diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 5b75319..ef72bae 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -355,6 +355,7 @@
 size_t strnlen(const char *s, size_t maxlen);
 unsigned int atou(const char *s);
 unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base);
+size_t strlen(const char *s);
 
 /* tty.c */
 void puts(const char *);