diff --git a/lib/id3tag/string_util.rb b/lib/id3tag/string_util.rb
index ac69e49..4cd7c70 100644
--- a/lib/id3tag/string_util.rb
+++ b/lib/id3tag/string_util.rb
@@ -20,7 +20,7 @@ def self.undo_unsynchronization(input)
     end
 
     def self.cut_at_null_byte(string)
-      string.split(NULL_BYTE, 2).first
+      string.split(NULL_BYTE, 2).first.to_s
     end
 
     def self.split_by_null_byte(string)
diff --git a/spec/lib/id3tag/string_util_spec.rb b/spec/lib/id3tag/string_util_spec.rb
index af56c97..52ecb6d 100644
--- a/spec/lib/id3tag/string_util_spec.rb
+++ b/spec/lib/id3tag/string_util_spec.rb
@@ -47,6 +47,21 @@
     end
   end
 
+  describe "cut_at_null_byte" do
+    let(:input) { }
+    subject { described_class.cut_at_null_byte(input) }
+
+    context 'when content is empty' do
+      let(:input) { '' }
+      it { is_expected.to eq('') }
+    end
+
+    context 'when content is present' do
+      let(:input) { "a\u0000b" }
+      it { is_expected.to eq('a') }
+    end
+  end
+
   describe "split_by_null_byte" do
     let(:input) { }
     subject { described_class.split_by_null_byte(input) }