diff --git a/lib/xmet/raob.py b/lib/xmet/raob.py
index 0348a7e..1959fd8 100644
--- a/lib/xmet/raob.py
+++ b/lib/xmet/raob.py
@@ -14,6 +14,11 @@ class RAOBReaderException(Exception):
     ...
 
 class RAOBSample():
+    __slots__ = (
+        'surface', 'height', 'pressure', 'temp', 'dewpoint',
+        'wind_dir', 'wind_speed'
+    )
+
     def __init__(self):
         self.surface:    bool  = False
         self.height:     float = None