diff --git a/sha1_file.c b/sha1_file.c
index c304522519..3466969344 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -903,10 +903,12 @@ static unsigned long get_delta_base(struct packed_git *p,
 	unsigned char *base_info = use_pack(p, w_curs, offset, NULL);
 	unsigned long base_offset;
 
-	/* there must be at least 20 bytes left regardless of delta type */
-	if (p->pack_size <= offset + 20)
-		die("truncated pack file");
-
+	/* use_pack() assured us we have [base_info, base_info + 20)
+	 * as a range that we can look at without walking off the
+	 * end of the mapped window.  Its actually the hash size
+	 * that is assured.  An OFS_DELTA longer than the hash size
+	 * is stupid, as then a REF_DELTA would be smaller to store.
+	 */
 	if (kind == OBJ_OFS_DELTA) {
 		unsigned used = 0;
 		unsigned char c = base_info[used++];
@@ -1009,6 +1011,12 @@ static unsigned long unpack_object_header(struct packed_git *p,
 	unsigned int left;
 	unsigned long used;
 
+	/* use_pack() assures us we have [base, base + 20) available
+	 * as a range that we can look at at.  (Its actually the hash
+	 * size that is assurred.)  With our object header encoding
+	 * the maximum deflated object size is 2^137, which is just
+	 * insane, so we know won't exceed what we have been given.
+	 */
 	base = use_pack(p, w_curs, offset, &left);
 	used = unpack_object_header_gently(base, left, type, sizep);
 	if (!used)