diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 31a674dd2674..f90f09682977 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -381,6 +381,9 @@ int num_to_str(char *buf, int size, unsigned long long num, unsigned int width)
 #define SMALL	32		/* use lowercase in hex (must be 32 == 0x20) */
 #define SPECIAL	64		/* prefix hex with "0x", octal with "0" */
 
+static_assert(ZEROPAD == ('0' - ' '));
+static_assert(SMALL == ' ');
+
 enum format_type {
 	FORMAT_TYPE_NONE, /* Just a string part */
 	FORMAT_TYPE_WIDTH,
@@ -507,7 +510,7 @@ char *number(char *buf, char *end, unsigned long long num,
 	/* zero or space padding */
 	if (!(spec.flags & LEFT)) {
 		char c = ' ' + (spec.flags & ZEROPAD);
-		BUILD_BUG_ON(' ' + ZEROPAD != '0');
+
 		while (--field_width >= 0) {
 			if (buf < end)
 				*buf = c;