diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 9ca0203922..96b110445d 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -721,7 +721,7 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
 	assert(data || obj_entry);
 
 	read_lock();
-	collision_test_needed = has_sha1_file(sha1);
+	collision_test_needed = has_sha1_file_with_flags(sha1, HAS_SHA1_QUICK);
 	read_unlock();
 
 	if (collision_test_needed && !data) {
diff --git a/cache.h b/cache.h
index f23fdbee96..3fb7570671 100644
--- a/cache.h
+++ b/cache.h
@@ -873,8 +873,17 @@ extern int has_sha1_pack(const unsigned char *sha1);
  * Return true iff we have an object named sha1, whether local or in
  * an alternate object database, and whether packed or loose.  This
  * function does not respect replace references.
+ *
+ * If the QUICK flag is set, do not re-check the pack directory
+ * when we cannot find the object (this means we may give a false
+ * negative answer if another process is simultaneously repacking).
  */
-extern int has_sha1_file(const unsigned char *sha1);
+#define HAS_SHA1_QUICK 0x1
+extern int has_sha1_file_with_flags(const unsigned char *sha1, int flags);
+static inline int has_sha1_file(const unsigned char *sha1)
+{
+	return has_sha1_file_with_flags(sha1, 0);
+}
 
 /*
  * Return true iff an alternate object database has a loose object
diff --git a/sha1_file.c b/sha1_file.c
index a38854ce55..18d0bfb8ac 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -3017,7 +3017,7 @@ int has_sha1_pack(const unsigned char *sha1)
 	return find_pack_entry(sha1, &e);
 }
 
-int has_sha1_file(const unsigned char *sha1)
+int has_sha1_file_with_flags(const unsigned char *sha1, int flags)
 {
 	struct pack_entry e;
 
@@ -3025,6 +3025,8 @@ int has_sha1_file(const unsigned char *sha1)
 		return 1;
 	if (has_loose_object(sha1))
 		return 1;
+	if (flags & HAS_SHA1_QUICK)
+		return 0;
 	reprepare_packed_git();
 	return find_pack_entry(sha1, &e);
 }