diff --git a/fileformats/core/fileset.py b/fileformats/core/fileset.py
index 9f42e428..b15e0e07 100644
--- a/fileformats/core/fileset.py
+++ b/fileformats/core/fileset.py
@@ -1167,7 +1167,7 @@ def sample(
                 mime_like = cls.mime_like
             except FormatDefinitionError:
                 mime_like = cls.__module__ + "." + cls.__name__
-            raise FormatMismatchError(
+            raise NotImplementedError(
                 f"File paths generated by override of FileSet.generate_sample_data() "
                 f"({fspaths}) do not match '{mime_like}' file type. A more specific "
                 f"implementation is required. Reason:\n\n{e}"