diff --git a/c_src/index.c b/c_src/index.c
index 2c7264f..ab8586a 100644
--- a/c_src/index.c
+++ b/c_src/index.c
@@ -107,15 +107,14 @@ geef_index_add(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[])
 	if (!enif_get_tuple(env, argv[1], &arity, &eentry))
 		return enif_make_badarg(env);
 
-	if (arity != 13)
-		return enif_make_badarg(env);
-
-	/* TODO: check for the 'tree_entry' tag */
 	memset(&entry, 0, sizeof(entry));
 
 	if (!enif_get_uint(env, eentry[5], &entry.mode))
 		return enif_make_badarg(env);
 
+	if (!enif_get_int64(env, eentry[8], &entry.file_size))
+		return enif_make_badarg(env);
+
 	if (!enif_inspect_iolist_as_binary(env, eentry[12], &path))
 		return enif_make_badarg(env);
 
@@ -152,7 +151,7 @@ geef_index_count(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[])
 ERL_NIF_TERM entry_to_term(ErlNifEnv *env, const git_index_entry *entry)
 {
 	ErlNifBinary id, path;
-	ERL_NIF_TERM mode;
+	ERL_NIF_TERM mode, file_size;
 	size_t len;
 
 	if (geef_oid_bin(&id, &entry->oid) < 0)
@@ -166,9 +165,10 @@ ERL_NIF_TERM entry_to_term(ErlNifEnv *env, const git_index_entry *entry)
 	memcpy(path.data, entry->path, len);
 
 	mode = enif_make_uint(env, entry->mode);
+	file_size = enif_make_int64(env, entry->file_size);
 
-	return enif_make_tuple4(env, atoms.ok, enif_make_binary(env, &path), enif_make_binary(env, &id),
-				mode);
+	return enif_make_tuple5(env, atoms.ok, enif_make_binary(env, &path), enif_make_binary(env, &id),
+				mode, file_size);
 }
 
 ERL_NIF_TERM
diff --git a/src/geef_index.erl b/src/geef_index.erl
index cdee3a9..0bc1d38 100644
--- a/src/geef_index.erl
+++ b/src/geef_index.erl
@@ -74,8 +74,8 @@ get(Pid, Path, Stage) ->
 nth(Pid, Nth) ->
     maybe_entry(gen_server:call(Pid, {nth, Nth})).
 
-maybe_entry({ok, Path, Id, Mode}) ->
-    {ok, #geef_index_entry{path=Path, id=#geef_oid{oid=Id}, mode=Mode}};
+maybe_entry({ok, Path, Id, Mode, Size}) ->
+    {ok, #geef_index_entry{path=Path, id=#geef_oid{oid=Id}, mode=Mode, size=Size}};
 maybe_entry(Error = {error, _}) ->
     Error.
 
@@ -136,7 +136,7 @@ handle_call({get, Path, Stage}, _From, State = #state{handle=Handle}) ->
     Reply = geef_nif:index_get(Handle, Path, Stage),
     {reply, Reply, State};
 
-handle_call({add, Entry}, _From, State = #state{handle=Handle}) ->
+handle_call({add, Entry = #geef_index_entry{}}, _From, State = #state{handle=Handle}) ->
     Reply = geef_nif:index_add(Handle, Entry),
     {reply, Reply, State}.
 
diff --git a/src/geef_records.hrl b/src/geef_records.hrl
index 433eaff..c7c2534 100644
--- a/src/geef_records.hrl
+++ b/src/geef_records.hrl
@@ -5,7 +5,7 @@
 	{ctime :: non_neg_integer(), mtime :: non_neg_integer(),
 	 dev :: non_neg_integer(), ino :: non_neg_integer(),
 	 mode :: non_neg_integer(), uid :: non_neg_integer(), gid :: non_neg_integer(),
-	 size :: non_neg_integer(),
+	 size = 0 :: non_neg_integer(),
 	 id :: geef_oid:oid(),
 	 flags, flags_extended,
 	 path :: iolist()}).
diff --git a/test/repo_test.erl b/test/repo_test.erl
index 28213f0..071b0aa 100644
--- a/test/repo_test.erl
+++ b/test/repo_test.erl
@@ -30,13 +30,14 @@ index_add_test(Repo) ->
     {ok, Odb} = geef_repo:odb(Repo),
     {ok, BlobId} = geef_odb:write(Odb, Data, blob),
     {ok, Idx} = geef_index:new(),
-    Entry = #geef_index_entry{mode=8#100644, id=BlobId, path="README"},
+    Entry = #geef_index_entry{mode=8#100644, id=BlobId, path="README", size=size(Data)},
     ok = geef_index:add(Idx, Entry),
     {ok, TreeId} = geef_index:write_tree(Idx, Repo),
     Expected = geef_oid:parse("5a20bbbf65ea75ad4d9f995d179156824ccca3a1"),
     {ok, Entry1} = geef_index:get(Idx, "README", 0),
     [?_assertEqual(Expected, TreeId),
      ?_assertEqual(BlobId, Entry1#geef_index_entry.id),
+     ?_assertEqual(size(Data), Entry1#geef_index_entry.size),
      ?_assertEqual(geef_index:count(Idx), 1)].
 
 ref_test(Repo) ->