diff --git a/midx.c b/midx.c
index 8cb063023c..76322b713c 100644
--- a/midx.c
+++ b/midx.c
@@ -307,13 +307,9 @@ int fill_midx_entry(struct repository * r,
 	if (!is_pack_valid(p))
 		return 0;
 
-	if (p->num_bad_objects) {
-		uint32_t i;
-		for (i = 0; i < p->num_bad_objects; i++)
-			if (hasheq(oid->hash,
-				   p->bad_object_sha1 + the_hash_algo->rawsz * i))
-				return 0;
-	}
+	if (oidset_size(&p->bad_objects) &&
+	    oidset_contains(&p->bad_objects, oid))
+		return 0;
 
 	e->offset = nth_midxed_offset(m, pos);
 	e->p = p;
diff --git a/object-store.h b/object-store.h
index b4dc6668aa..c7bead66f6 100644
--- a/object-store.h
+++ b/object-store.h
@@ -10,6 +10,7 @@
 #include "khash.h"
 #include "dir.h"
 #include "oidtree.h"
+#include "oidset.h"
 
 struct object_directory {
 	struct object_directory *next;
@@ -75,9 +76,8 @@ struct packed_git {
 	const void *index_data;
 	size_t index_size;
 	uint32_t num_objects;
-	uint32_t num_bad_objects;
 	uint32_t crc_offset;
-	unsigned char *bad_object_sha1;
+	struct oidset bad_objects;
 	int index_version;
 	time_t mtime;
 	int pack_fd;
diff --git a/packfile.c b/packfile.c
index 04080a558b..caba29c624 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1163,29 +1163,17 @@ int unpack_object_header(struct packed_git *p,
 
 void mark_bad_packed_object(struct packed_git *p, const struct object_id *oid)
 {
-	unsigned i;
-	const unsigned hashsz = the_hash_algo->rawsz;
-	for (i = 0; i < p->num_bad_objects; i++)
-		if (hasheq(oid->hash, p->bad_object_sha1 + hashsz * i))
-			return;
-	p->bad_object_sha1 = xrealloc(p->bad_object_sha1,
-				      st_mult(GIT_MAX_RAWSZ,
-					      st_add(p->num_bad_objects, 1)));
-	hashcpy(p->bad_object_sha1 + hashsz * p->num_bad_objects, oid->hash);
-	p->num_bad_objects++;
+	oidset_insert(&p->bad_objects, oid);
 }
 
 const struct packed_git *has_packed_and_bad(struct repository *r,
 					    const struct object_id *oid)
 {
 	struct packed_git *p;
-	unsigned i;
 
 	for (p = r->objects->packed_git; p; p = p->next)
-		for (i = 0; i < p->num_bad_objects; i++)
-			if (hasheq(oid->hash,
-				   p->bad_object_sha1 + the_hash_algo->rawsz * i))
-				return p;
+		if (oidset_contains(&p->bad_objects, oid))
+			return p;
 	return NULL;
 }
 
@@ -2016,13 +2004,9 @@ static int fill_pack_entry(const struct object_id *oid,
 {
 	off_t offset;
 
-	if (p->num_bad_objects) {
-		unsigned i;
-		for (i = 0; i < p->num_bad_objects; i++)
-			if (hasheq(oid->hash,
-				   p->bad_object_sha1 + the_hash_algo->rawsz * i))
-				return 0;
-	}
+	if (oidset_size(&p->bad_objects) &&
+	    oidset_contains(&p->bad_objects, oid))
+		return 0;
 
 	offset = find_pack_entry_one(oid->hash, p);
 	if (!offset)