diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 5b7531966b84..ef72baeff484 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -355,6 +355,7 @@ int strncmp(const char *cs, const char *ct, size_t count);
 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 *);
diff --git a/arch/x86/boot/printf.c b/arch/x86/boot/printf.c
index cdac91ca55d3..565083c16e5c 100644
--- a/arch/x86/boot/printf.c
+++ b/arch/x86/boot/printf.c
@@ -55,7 +55,7 @@ static char *number(char *str, long num, int base, int size, int precision,
 	locase = (type & SMALL);
 	if (type & LEFT)
 		type &= ~ZEROPAD;
-	if (base < 2 || base > 36)
+	if (base < 2 || base > 16)
 		return NULL;
 	c = (type & ZEROPAD) ? '0' : ' ';
 	sign = 0;