diff --git a/src/main/java/eu/siacs/conversations/utils/MimeUtils.java b/src/main/java/eu/siacs/conversations/utils/MimeUtils.java
index a9e89d1b716ce67866d012fa459fc8a40fbc0c65..d45444240732d9445e4899a17d7c4431366a583a 100644
--- a/src/main/java/eu/siacs/conversations/utils/MimeUtils.java
+++ b/src/main/java/eu/siacs/conversations/utils/MimeUtils.java
@@ -458,7 +458,7 @@ public final class MimeUtils {
         if (extension == null || extension.isEmpty()) {
             return null;
         }
-        return extensionToMimeTypeMap.get(extension);
+        return extensionToMimeTypeMap.get(extension.toLowerCase());
     }
     /**
      * Returns true if the given extension has a registered MIME type.