diff --git a/src/postprocessor/chainer.py b/src/postprocessor/chainer.py
index 4b101922ee882744ee7d1e311a3b35bbe7f9bdec..831d5471b558cd574410d1b0d538de98838e7403 100644
--- a/src/postprocessor/chainer.py
+++ b/src/postprocessor/chainer.py
@@ -43,7 +43,7 @@ class Chainer(Signal):
                 replace_path(denominator, alias + bgsub), **kwargs
             )
             / self.get(replace_path(numerator, alias + bgsub), **kwargs)
-            for alias, (denominator, numerator) in self.synonyms.items()
+            for alias, (denominator, numerator) in self._synonyms.items()
             for bgsub in ("", "_bgsub")
         }