diff --git a/numpydoc/validate.py b/numpydoc/validate.py
index 30b0f413..9b17efaf 100644
--- a/numpydoc/validate.py
+++ b/numpydoc/validate.py
@@ -328,7 +328,7 @@ def source_file_def_line(self):
             def_line = next(
                 i
                 for i, x in enumerate(
-                    re.match("^ *(def|class) ", s) for s in sourcelines[0]
+                    re.match(r"^\s*(async\s+)?(?:def|class)\s+", s) for s in sourcelines[0]
                 )
                 if x is not None
             )