diff --git a/arch/x86/boot/printf.c b/arch/x86/boot/printf.c
index c1d00c02..50e47cd 100644
--- a/arch/x86/boot/printf.c
+++ b/arch/x86/boot/printf.c
@@ -56,7 +56,7 @@
 	if (type & LEFT)
 		type &= ~ZEROPAD;
 	if (base < 2 || base > 36)
-		return 0;
+		return NULL;
 	c = (type & ZEROPAD) ? '0' : ' ';
 	sign = 0;
 	if (type & SIGN) {