diff --git a/lib/parser.c b/lib/parser.c
index fb34977..6e89eca 100644
--- a/lib/parser.c
+++ b/lib/parser.c
@@ -128,12 +128,13 @@
 	char *endp;
 	char *buf;
 	int ret;
+	size_t len = s->to - s->from;
 
-	buf = kmalloc(s->to - s->from + 1, GFP_KERNEL);
+	buf = kmalloc(len + 1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
-	memcpy(buf, s->from, s->to - s->from);
-	buf[s->to - s->from] = '\0';
+	memcpy(buf, s->from, len);
+	buf[len] = '\0';
 	*result = simple_strtol(buf, &endp, base);
 	ret = 0;
 	if (endp == buf)