diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index cccd0f8040d0222e3f343dc06b8830758511681e..88d2bb8153e86ccbaa65d93008d5075cebc3ddc7 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -34,10 +34,12 @@
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
 #define SET_SIZE(obj,size) oe_set_size(&to_pack, obj, size)
+#define DELTA_SIZE(obj) oe_delta_size(&to_pack, obj)
 #define DELTA(obj) oe_delta(&to_pack, obj)
 #define DELTA_CHILD(obj) oe_delta_child(&to_pack, obj)
 #define DELTA_SIBLING(obj) oe_delta_sibling(&to_pack, obj)
 #define SET_DELTA(obj, val) oe_set_delta(&to_pack, obj, val)
+#define SET_DELTA_SIZE(obj, val) oe_set_delta_size(&to_pack, obj, val)
 #define SET_DELTA_CHILD(obj, val) oe_set_delta_child(&to_pack, obj, val)
 #define SET_DELTA_SIBLING(obj, val) oe_set_delta_sibling(&to_pack, obj, val)
 
@@ -144,7 +146,7 @@ static void *get_delta(struct object_entry *entry)
 		    oid_to_hex(&DELTA(entry)->idx.oid));
 	delta_buf = diff_delta(base_buf, base_size,
 			       buf, size, &delta_size, 0);
-	if (!delta_buf || delta_size != entry->delta_size)
+	if (!delta_buf || delta_size != DELTA_SIZE(entry))
 		die("delta size changed");
 	free(buf);
 	free(base_buf);
@@ -294,14 +296,14 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 		FREE_AND_NULL(entry->delta_data);
 		entry->z_delta_size = 0;
 	} else if (entry->delta_data) {
-		size = entry->delta_size;
+		size = DELTA_SIZE(entry);
 		buf = entry->delta_data;
 		entry->delta_data = NULL;
 		type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
 			OBJ_OFS_DELTA : OBJ_REF_DELTA;
 	} else {
 		buf = get_delta(entry);
-		size = entry->delta_size;
+		size = DELTA_SIZE(entry);
 		type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
 			OBJ_OFS_DELTA : OBJ_REF_DELTA;
 	}
@@ -1509,7 +1511,7 @@ static void check_object(struct object_entry *entry)
 			oe_set_type(entry, entry->in_pack_type);
 			SET_SIZE(entry, in_pack_size); /* delta size */
 			SET_DELTA(entry, base_entry);
-			entry->delta_size = in_pack_size;
+			SET_DELTA_SIZE(entry, in_pack_size);
 			entry->delta_sibling_idx = base_entry->delta_child_idx;
 			SET_DELTA_CHILD(base_entry, entry);
 			unuse_pack(&w_curs);
@@ -1937,7 +1939,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 		max_size = trg_size/2 - 20;
 		ref_depth = 1;
 	} else {
-		max_size = trg_entry->delta_size;
+		max_size = DELTA_SIZE(trg_entry);
 		ref_depth = trg->depth;
 	}
 	max_size = (uint64_t)max_size * (max_depth - src->depth) /
@@ -2006,10 +2008,14 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	delta_buf = create_delta(src->index, trg->data, trg_size, &delta_size, max_size);
 	if (!delta_buf)
 		return 0;
+	if (delta_size >= (1U << OE_DELTA_SIZE_BITS)) {
+		free(delta_buf);
+		return 0;
+	}
 
 	if (DELTA(trg_entry)) {
 		/* Prefer only shallower same-sized deltas. */
-		if (delta_size == trg_entry->delta_size &&
+		if (delta_size == DELTA_SIZE(trg_entry) &&
 		    src->depth + 1 >= trg->depth) {
 			free(delta_buf);
 			return 0;
@@ -2024,7 +2030,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	free(trg_entry->delta_data);
 	cache_lock();
 	if (trg_entry->delta_data) {
-		delta_cache_size -= trg_entry->delta_size;
+		delta_cache_size -= DELTA_SIZE(trg_entry);
 		trg_entry->delta_data = NULL;
 	}
 	if (delta_cacheable(src_size, trg_size, delta_size)) {
@@ -2037,7 +2043,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	}
 
 	SET_DELTA(trg_entry, src_entry);
-	trg_entry->delta_size = delta_size;
+	SET_DELTA_SIZE(trg_entry, delta_size);
 	trg->depth = src->depth + 1;
 
 	return 1;
@@ -2160,11 +2166,11 @@ static void find_deltas(struct object_entry **list, unsigned *list_size,
 		if (entry->delta_data && !pack_to_stdout) {
 			unsigned long size;
 
-			size = do_compress(&entry->delta_data, entry->delta_size);
+			size = do_compress(&entry->delta_data, DELTA_SIZE(entry));
 			if (size < (1U << OE_Z_DELTA_BITS)) {
 				entry->z_delta_size = size;
 				cache_lock();
-				delta_cache_size -= entry->delta_size;
+				delta_cache_size -= DELTA_SIZE(entry);
 				delta_cache_size += entry->z_delta_size;
 				cache_unlock();
 			} else {
diff --git a/pack-objects.h b/pack-objects.h
index ee2c7ab382b64d56e9021c3a9022b7531e55724a..1c588184b28658f9fdaee458019b9c81e5e8f252 100644
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -12,6 +12,7 @@
  * above this limit. Don't lower it too much.
  */
 #define OE_SIZE_BITS		31
+#define OE_DELTA_SIZE_BITS	20
 
 /*
  * State flags for depth-first search used for analyzing delta cycles.
@@ -85,7 +86,8 @@ struct object_entry {
 				     * uses the same base as me
 				     */
 	void *delta_data;	/* cached delta (uncompressed) */
-	unsigned long delta_size;	/* delta data size (uncompressed) */
+	unsigned delta_size_:OE_DELTA_SIZE_BITS; /* delta data size (uncompressed) */
+	unsigned delta_size_valid:1;
 	unsigned z_delta_size:OE_Z_DELTA_BITS;
 	unsigned type_:TYPE_BITS;
 	unsigned in_pack_type:TYPE_BITS; /* could be delta */
@@ -309,4 +311,23 @@ static inline void oe_set_size(struct packing_data *pack,
 	}
 }
 
+static inline unsigned long oe_delta_size(struct packing_data *pack,
+					  const struct object_entry *e)
+{
+	if (e->delta_size_valid)
+		return e->delta_size_;
+	return oe_size(pack, e);
+}
+
+static inline void oe_set_delta_size(struct packing_data *pack,
+				     struct object_entry *e,
+				     unsigned long size)
+{
+	e->delta_size_ = size;
+	e->delta_size_valid = e->delta_size_ == size;
+	if (!e->delta_size_valid && size != oe_size(pack, e))
+		BUG("this can only happen in check_object() "
+		    "where delta size is the same as entry size");
+}
+
 #endif