diff --git a/.gitignore b/.gitignore
index ef96859..0fd4137 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 /dehub
+*/git-http-server
diff --git a/cmd/git-http-server/main.go b/cmd/git-http-server/main.go
index 0430c23..7a842b4 100644
--- a/cmd/git-http-server/main.go
+++ b/cmd/git-http-server/main.go
@@ -25,6 +25,32 @@ type handler struct {
 	tpl    *template.Template
 }
 
+func (h handler) getTree(r *http.Request) (*object.Tree, int, error) {
+	rev := plumbing.Revision(r.FormValue("rev"))
+	if rev == "" {
+		rev = plumbing.Revision(h.branch)
+	}
+
+	hashPtr, err := h.repo.ResolveRevision(rev)
+	if err != nil {
+		return nil, 404, fmt.Errorf("resolving revision %q: %w", rev, err)
+	}
+	hash := *hashPtr // I don't know why ResolveRevision returns a pointer
+
+	commit, err := h.repo.CommitObject(hash)
+	if err != nil {
+		return nil, 404, fmt.Errorf("retrieving commit for revision %q (%q): %w",
+			rev, hash, err)
+	}
+
+	tree, err := h.repo.TreeObject(commit.TreeHash)
+	if err != nil {
+		return nil, 500, fmt.Errorf("fetching tree %q of commit %q: %v",
+			commit.TreeHash, hash, err)
+	}
+	return tree, 0, nil
+}
+
 func (h handler) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
 	path := r.URL.Path
 	var mdPath string
@@ -42,28 +68,9 @@ func (h handler) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
 	path = strings.TrimPrefix(path, "/")
 	mdPath = strings.TrimPrefix(mdPath, "/")
 
-	ref, err := h.repo.Reference(h.branch, true)
-	if errors.Is(err, plumbing.ErrReferenceNotFound) {
-		http.Error(rw, "branch does not exist", 404)
-		return
-	} else if err != nil {
-		log.Printf("resolving reference %q: %v", h.branch, err)
-		http.Error(rw, "internal error", 500)
-		return
-	}
-
-	hash := ref.Hash()
-	commit, err := h.repo.CommitObject(hash)
+	tree, errStatusCode, err := h.getTree(r)
 	if err != nil {
-		log.Printf("fetching commit %q: %v", hash, err)
-		http.Error(rw, "internal error", 500)
-		return
-	}
-
-	tree, err := h.repo.TreeObject(commit.TreeHash)
-	if err != nil {
-		log.Printf("fetching tree %q of commit %q: %v", commit.TreeHash, hash, err)
-		http.Error(rw, "internal error", 500)
+		http.Error(rw, err.Error(), errStatusCode)
 		return
 	}