diff --git a/homeassistant/helpers/json.py b/homeassistant/helpers/json.py
index 0589490d2748..6a0792383cb6 100644
--- a/homeassistant/helpers/json.py
+++ b/homeassistant/helpers/json.py
@@ -122,10 +122,11 @@ def cached_json_bytes(data: Any) -> bytes:
     orjson over-allocates the returned bytes buffer and does not shrink it: the
     logical length is set but the capacity is rounded up to a power of two (at
     least a few KiB), so bytes cached for the lifetime of a long-lived object
-    retain several KiB of unused buffer.
+    retain several KiB of unused buffer. Copy them into a right-sized buffer.
     """
-    # Drop orjson's over-allocated slack with help of a memoryview.
-    return bytes(memoryview(json_bytes(data)))
+    # The empty second join item is load-bearing: it forces a copy into a
+    # right-sized buffer; a single-item join returns the input unchanged.
+    return b"".join((json_bytes(data), b""))
 
 
 def cached_json_fragment(data: Any) -> orjson.Fragment:
@@ -134,8 +135,9 @@ def cached_json_fragment(data: Any) -> orjson.Fragment:
     Wraps the same right-sized bytes as cached_json_bytes; the body is inlined
     rather than calling it to avoid an extra function call on this hot path.
     """
-    # Drop orjson's over-allocated slack with help of a memoryview.
-    return orjson.Fragment(bytes(memoryview(json_bytes(data))))
+    # The empty second join item is load-bearing: it forces a copy into a
+    # right-sized buffer; a single-item join returns the input unchanged.
+    return orjson.Fragment(b"".join((json_bytes(data), b"")))
 
 
 def json_dumps(data: Any) -> str: