diff --git a/FileTypeChecker.Tests/FileTypeChecker.Tests.csproj b/FileTypeChecker.Tests/FileTypeChecker.Tests.csproj
index 36876c8..d6f99ac 100644
--- a/FileTypeChecker.Tests/FileTypeChecker.Tests.csproj
+++ b/FileTypeChecker.Tests/FileTypeChecker.Tests.csproj
@@ -113,6 +113,9 @@
     <None Update="files\365-doc-empty.docx">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Update="files\365-issue311.docx">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <None Update="files\test-offset.mp4">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
diff --git a/FileTypeChecker.Tests/FileTypeValidatorTests.cs b/FileTypeChecker.Tests/FileTypeValidatorTests.cs
index 3946cfe..86f026c 100644
--- a/FileTypeChecker.Tests/FileTypeValidatorTests.cs
+++ b/FileTypeChecker.Tests/FileTypeValidatorTests.cs
@@ -257,6 +257,7 @@ public void Is_ShouldReturnFalseIfTypesDidNotMatch()
         [TestCase("test.ico", typeof(Icon))]
         [TestCase("365-doc.docx", typeof(MicrosoftOffice365Document))]
         [TestCase("365-doc-empty.docx", typeof(MicrosoftOffice365Document))]
+        [TestCase("365-issue311.docx", typeof(MicrosoftOffice365Document))]
         [TestCase("testwin10.zip", typeof(ZipFile))]
         [TestCase("test.webp", typeof(Webp))]
         [TestCase("sample.heic", typeof(HighEfficiencyImageFile))]
diff --git a/FileTypeChecker.Tests/files/365-issue311.docx b/FileTypeChecker.Tests/files/365-issue311.docx
new file mode 100644
index 0000000..e4328ec
Binary files /dev/null and b/FileTypeChecker.Tests/files/365-issue311.docx differ