diff --git a/ErsatzTV.Core.Tests/FFmpeg/CustomStreamSelectorTests.cs b/ErsatzTV.Core.Tests/FFmpeg/CustomStreamSelectorTests.cs
index d9a34cbf1..5f1f0009e 100644
--- a/ErsatzTV.Core.Tests/FFmpeg/CustomStreamSelectorTests.cs
+++ b/ErsatzTV.Core.Tests/FFmpeg/CustomStreamSelectorTests.cs
@@ -67,6 +67,31 @@ items:
             }
         }
 
+        [Test]
+        public async Task Should_Select_und_Audio_Missing_Language()
+        {
+            const string YAML =
+"""
+---
+items:
+  - audio_language: ["und"]
+""";
+
+            var streamSelector = new CustomStreamSelector(
+                new FakeLocalFileSystem([new FakeFileEntry(TestFileName) { Contents = YAML }]),
+                new NullLogger<CustomStreamSelector>());
+
+            StreamSelectorResult result = await streamSelector.SelectStreams(_channel, _audioVersion, _subtitles);
+
+            result.AudioStream.IsSome.ShouldBeTrue();
+
+            foreach (MediaStream audioStream in result.AudioStream)
+            {
+                audioStream.Index.ShouldBe(3);
+                audioStream.Language.ShouldBeNullOrWhiteSpace();
+            }
+        }
+
         [Test]
         public async Task Should_Select_eng_Audio_Exact_Match_Multiple_Audio_Languages()
         {
@@ -690,7 +715,13 @@ items:
                         Channels = 6,
                         Language = englishLanguage,
                         Title = "Movie Title",
-                        Default = true
+                    },
+                    new MediaStream
+                    {
+                        Index = 3,
+                        MediaStreamKind = MediaStreamKind.Audio,
+                        Channels = 2,
+                        Title = "Who Knows",
                     }
                 ]
             };
diff --git a/ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs b/ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs
index 597fd2dda..13609f90f 100644
--- a/ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs
+++ b/ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs
@@ -43,7 +43,8 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
                 foreach (MediaStream audioStream in audioStreams.ToList())
                 {
                     var matches = false;
-                    string safeTitle = audioStream.Title ?? string.Empty;
+                    string safeTitle = (audioStream.Title ?? string.Empty).ToLowerInvariant();
+                    string safeLanguage = (audioStream.Language ?? "und").ToLowerInvariant();
 
                     if (streamSelectorItem.AudioLanguages.Count > 0)
                     {
@@ -60,7 +61,7 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
 
                             matches = matches || FileSystemName.MatchesSimpleExpression(
                                 audioLanguage.ToLowerInvariant(),
-                                audioStream.Language.ToLowerInvariant());
+                                safeLanguage);
 
                             // store lang index for prioritizing later
                             if (matches && candidateAudioStreams[audioStream] == int.MaxValue)
@@ -105,7 +106,7 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
 
                         logger.LogDebug(
                             "Audio stream {@Stream} does not match selector item {@SelectorItem}",
-                            new { audioStream.Language, audioStream.Title },
+                            new { Language = safeLanguage, Title = safeTitle },
                             streamSelectorItem);
                     }
                     else
@@ -114,7 +115,7 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
 
                         logger.LogDebug(
                             "Audio stream {@Stream} matches selector item {@SelectorItem}",
-                            new { audioStream.Language, audioStream.Title },
+                            new { Language = safeLanguage, Title = safeTitle },
                             streamSelectorItem);
                     }
                 }
@@ -130,7 +131,8 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
                     foreach (Subtitle subtitle in allSubtitles.ToList())
                     {
                         var matches = false;
-                        string safeTitle = subtitle.Title ?? string.Empty;
+                        string safeTitle = (subtitle.Title ?? string.Empty).ToLowerInvariant();
+                        string safeLanguage = (subtitle.Language ?? "und").ToLowerInvariant();
 
                         if (streamSelectorItem.SubtitleLanguages.Count > 0)
                         {
@@ -147,7 +149,7 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
 
                                 matches = matches || FileSystemName.MatchesSimpleExpression(
                                     subtitleLanguage,
-                                    subtitle.Language);
+                                    safeLanguage);
 
                                 // store lang index for prioritizing later
                                 if (matches && candidateSubtitles[subtitle] == int.MaxValue)
@@ -192,7 +194,7 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
 
                             logger.LogDebug(
                                 "Subtitle {@Subtitle} does not match selector item {@SelectorItem}",
-                                new { subtitle.Language, subtitle.Title },
+                                new { Language = safeLanguage, Title = safeTitle },
                                 streamSelectorItem);
                         }
                         else
@@ -201,7 +203,7 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
 
                             logger.LogDebug(
                                 "Subtitle {@Subtitle} matches selector item {@SelectorItem}",
-                                new { subtitle.Language, subtitle.Title },
+                                new { Language = safeLanguage, Title = safeTitle },
                                 streamSelectorItem);
                         }
                     }