diff --git a/homeassistant/util/dt.py b/homeassistant/util/dt.py
index 656f77b3289..a9a6ca4e3a3 100644
--- a/homeassistant/util/dt.py
+++ b/homeassistant/util/dt.py
@@ -79,10 +79,11 @@ def as_utc(dattim: dt.datetime) -> dt.datetime:
     return dattim.astimezone(UTC)
 
 
-def as_timestamp(dt_value: dt.datetime) -> float:
+def as_timestamp(dt_value: dt.datetime | str) -> float:
     """Convert a date/time into a unix time (seconds since 1970)."""
-    if hasattr(dt_value, "timestamp"):
-        parsed_dt: dt.datetime | None = dt_value
+    parsed_dt: dt.datetime | None
+    if isinstance(dt_value, dt.datetime):
+        parsed_dt = dt_value
     else:
         parsed_dt = parse_datetime(str(dt_value))
     if parsed_dt is None: