diff --git a/plugin/commands/auto_set_syntax.py b/plugin/commands/auto_set_syntax.py
index 1116f8a0..644fdc17 100644
--- a/plugin/commands/auto_set_syntax.py
+++ b/plugin/commands/auto_set_syntax.py
@@ -132,10 +132,10 @@ def _assign_syntax_for_new_view(view_snapshot: ViewSnapshot, event: ListenerEven
 def _assign_syntax_for_st_syntax_test(view_snapshot: ViewSnapshot, event: ListenerEvent | None = None) -> bool:
     if (
         (view := view_snapshot.valid_view)
-        and (not view_snapshot.syntax or is_plaintext_syntax(view_snapshot.syntax))
+        and ((view.file_name() or "").startswith("syntax_test_"))
         and (m := RE_ST_SYNTAX_TEST_LINE.search(view_snapshot.first_line))
-        and (new_syntax := m.group("syntax")).endswith(".sublime-syntax")
     ):
+        new_syntax: str = m.group("syntax")
         if syntax := find_syntax_by_syntax_like(new_syntax, include_hidden=True, include_plaintext=True):
             return assign_syntax_to_view(
                 view,