diff --git a/fileformats/core/datatype.py b/fileformats/core/datatype.py
index 3118948..530829c 100644
--- a/fileformats/core/datatype.py
+++ b/fileformats/core/datatype.py
@@ -263,7 +263,7 @@ def get_format(mime_name: str) -> ty.Type[DataType]:
                         f"Did not find '{class_name}' class in fileformats.{namespace} "
                         f"corresponding to MIME, or MIME-like, type {mime_string}"
                     ) from None
-        if not issubclass(klass, cls):
+        if not (ty.get_origin(klass) is ty.Union or issubclass(klass, cls)):
             raise FormatRecognitionError(
                 f"Class '{klass}' does not inherit from '{cls}'"
             )