diff --git a/vlib/builtin/int.v b/vlib/builtin/int.v
index 1bd004cb7c..93893ece0f 100644
--- a/vlib/builtin/int.v
+++ b/vlib/builtin/int.v
@@ -158,7 +158,7 @@ pub fn (n i64) hex() string {
 	hex := malloc(len)
 	// TODO
 	//count := C.sprintf(charptr(hex), '0x%'C.PRIx64, n)
-	count := C.sprintf(charptr(hex), '0x%llx', n)
+	count := C.sprintf(charptr(hex), C.V64_PRINTFORMAT, n)
 	return tos(hex, count)
 }
 
@@ -166,7 +166,7 @@ pub fn (n u64) hex() string {
 	len := if n > 0 { n.str().len + 3 } else { 19 }
 	hex := malloc(len)
 	//count := C.sprintf(charptr(hex), '0x%'C.PRIx64, n)
-	count := C.sprintf(charptr(hex), '0x%llx', n)
+	count := C.sprintf(charptr(hex), C.V64_PRINTFORMAT, n)
 	//count := C.sprintf(charptr(hex), '0x%lx', n)
 	return tos(hex, count)
 }