diff --git a/src/SIL.Machine/Corpora/ParatextProjectSettings.cs b/src/SIL.Machine/Corpora/ParatextProjectSettings.cs
index 28bdbbf4..1ff1dd90 100644
--- a/src/SIL.Machine/Corpora/ParatextProjectSettings.cs
+++ b/src/SIL.Machine/Corpora/ParatextProjectSettings.cs
@@ -89,8 +89,13 @@ public bool IsBookFileName(string fileName, out string bookId)
         {
             bookId = null;
 
-            if (!fileName.StartsWith(FileNamePrefix) || !fileName.EndsWith(FileNameSuffix))
+            if (
+                !fileName.StartsWith(FileNamePrefix, ignoreCase: true, CultureInfo.InvariantCulture)
+                || !fileName.EndsWith(FileNameSuffix, ignoreCase: true, CultureInfo.InvariantCulture)
+            )
+            {
                 return false;
+            }
 
             string bookPart = fileName.Substring(
                 FileNamePrefix.Length,
diff --git a/tests/SIL.Machine.Tests/Corpora/ParatextProjectSettingsTests.cs b/tests/SIL.Machine.Tests/Corpora/ParatextProjectSettingsTests.cs
index 63be4d01..4aa2b5d1 100644
--- a/tests/SIL.Machine.Tests/Corpora/ParatextProjectSettingsTests.cs
+++ b/tests/SIL.Machine.Tests/Corpora/ParatextProjectSettingsTests.cs
@@ -171,6 +171,14 @@ public void IsBookFileName_WrongBookPart_BookNumBookId()
         Assert.That(settings.IsBookFileName("PROJ100.SFM", out _), Is.False);
     }
 
+    [Test]
+    public void IsBookFileName_CaseInsensitive()
+    {
+        ParatextProjectSettings settings = CreateSettings("MAT");
+        Assert.That(settings.IsBookFileName("PROJMRK.sfm", out string bookId), Is.True);
+        Assert.That(bookId, Is.EqualTo("MRK"));
+    }
+
     private static ParatextProjectSettings CreateSettings(string fileNameForm)
     {
         return new ParatextProjectSettings(