diff --git a/vlib/builtin/int.v b/vlib/builtin/int.v
index 30a3aa50cc..c01b543e11 100644
--- a/vlib/builtin/int.v
+++ b/vlib/builtin/int.v
@@ -19,7 +19,7 @@ pub fn (nn int) str() string {
 		return '0'
 	}
 	max := 16
-	mut buf := calloc(max)
+	mut buf := calloc(max+1)
 	mut len := 0
 	mut is_neg := false
 	if n < 0 {
@@ -38,6 +38,7 @@ pub fn (nn int) str() string {
 		buf[max - len - 1] = `-`
 		len++
 	}
+	buf[max] = `\0`
 	return tos(buf + max - len, len)
 }