diff --git a/tree.go b/tree.go
index 8288176..eba9f3d 100644
--- a/tree.go
+++ b/tree.go
@@ -149,7 +149,7 @@
 	C.git_treebuilder_free(v.ptr)
 }
 
-func (v *TreeBuilder) Insert(filename string, id *Oid, filemode int) error {
+func (v *TreeBuilder) Insert(filename string, id *Oid, filemode Filemode) error {
 	cfilename := C.CString(filename)
 	defer C.free(unsafe.Pointer(cfilename))
 
diff --git a/tree_test.go b/tree_test.go
index 4c6a4ed..fae395a 100644
--- a/tree_test.go
+++ b/tree_test.go
@@ -20,3 +20,44 @@
 		t.Fatalf("entry id %v was not found", id)
 	}
 }
+
+func TestTreeBuilderInsert(t *testing.T) {
+	repo := createTestRepo(t)
+	defer cleanupTestRepo(t, repo)
+
+	subTree, err := repo.TreeBuilder()
+	if err != nil {
+		t.Fatalf("TreeBuilder: %v", err)
+	}
+	defer subTree.Free()
+
+	odb, err := repo.Odb()
+	if err != nil {
+		t.Fatalf("repo.Odb: %v", err)
+	}
+	blobId, err := odb.Write([]byte("hello"), ObjectBlob)
+	if err != nil {
+		t.Fatalf("odb.Write: %v", err)
+	}
+	if err = subTree.Insert("subfile", blobId, FilemodeBlobExecutable); err != nil {
+		t.Fatalf("TreeBuilder.Insert: %v", err)
+	}
+	treeID, err := subTree.Write()
+	if err != nil {
+		t.Fatalf("TreeBuilder.Write: %v", err)
+	}
+
+	tree, err := repo.LookupTree(treeID)
+	if err != nil {
+		t.Fatalf("LookupTree: %v", err)
+	}
+
+	entry, err := tree.EntryByPath("subfile")
+	if err != nil {
+		t.Fatalf("tree.EntryByPath(%q): %v", "subfile", err)
+	}
+
+	if !entry.Id.Equal(blobId) {
+		t.Fatalf("got oid %v, want %v", entry.Id, blobId)
+	}
+}