fix warnings
diff --git a/skeletons/BIT_STRING.h b/skeletons/BIT_STRING.h
index ffca5f7..f74c433 100644
--- a/skeletons/BIT_STRING.h
+++ b/skeletons/BIT_STRING.h
@@ -13,7 +13,7 @@
 
 typedef struct BIT_STRING_s {
 	uint8_t *buf;	/* BIT STRING body */
-	int size;	/* Size of the above buffer */
+	size_t size;	/* Size of the above buffer */
 
 	int bits_unused;/* Unused trailing bits in the last octet (0..7) */