diff --git a/index.go b/index.go
index dd13460..32acd14 100644
--- a/index.go
+++ b/index.go
@@ -90,7 +90,9 @@ func populateCIndexEntry(source *IndexEntry, dest *C.git_index_entry) {
 	dest.uid = C.uint32_t(source.Uid)
 	dest.gid = C.uint32_t(source.Gid)
 	dest.file_size = C.uint32_t(source.Size)
-	dest.id = *source.Id.toC()
+	if source.Id != nil {
+		dest.id = *source.Id.toC()
+	}
 	dest.path = C.CString(source.Path)
 }
 
@@ -195,6 +197,28 @@ func (v *Index) AddByPath(path string) error {
 	return nil
 }
 
+// AddFromBuffer adds or replaces an index entry from a buffer in memory
+func (v *Index) AddFromBuffer(entry *IndexEntry, buffer []byte) error {
+	var centry C.git_index_entry
+
+	populateCIndexEntry(entry, &centry)
+	defer freeCIndexEntry(&centry)
+
+	var cbuffer unsafe.Pointer
+	if len(buffer) > 0 {
+		cbuffer = unsafe.Pointer(&buffer[0])
+	}
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	if err := C.git_index_add_frombuffer(v.ptr, &centry, cbuffer, C.size_t(len(buffer))); err < 0 {
+		return MakeGitError(err)
+	}
+
+	return nil
+}
+
 func (v *Index) AddAll(pathspecs []string, flags IndexAddOpts, callback IndexMatchedPathCallback) error {
 	cpathspecs := C.git_strarray{}
 	cpathspecs.count = C.size_t(len(pathspecs))
diff --git a/index_test.go b/index_test.go
index f47dace..d882809 100644
--- a/index_test.go
+++ b/index_test.go
@@ -149,6 +149,30 @@ func TestIndexRemoveDirectory(t *testing.T) {
 	}
 }
 
+func TestIndexAddFromBuffer(t *testing.T) {
+	t.Parallel()
+	repo := createTestRepo(t)
+	defer cleanupTestRepo(t, repo)
+
+	idx, err := repo.Index()
+	checkFatal(t, err)
+
+	entry := IndexEntry{
+		Path: "README",
+		Mode: FilemodeBlob,
+	}
+
+	err = idx.AddFromBuffer(&entry, []byte("foo\n"))
+	checkFatal(t, err)
+
+	treeId, err := idx.WriteTreeTo(repo)
+	checkFatal(t, err)
+
+	if treeId.String() != "b7119b11e8ef7a1a5a34d3ac87f5b075228ac81e" {
+		t.Fatalf("%v", treeId.String())
+	}
+}
+
 func TestIndexAddAllNoCallback(t *testing.T) {
 	t.Parallel()
 	repo := createTestRepo(t)