diff --git a/docs/building/sources/perturbations.rst b/docs/building/sources/perturbations.rst
index 39fd72f4..f6ae8bf6 100644
--- a/docs/building/sources/perturbations.rst
+++ b/docs/building/sources/perturbations.rst
@@ -51,6 +51,11 @@ center
 .. literalinclude:: yaml/perturbations.yaml
    :language: yaml
 
+In this example, the `perturbations` function is applied using two
+:ref:`references <yaml-reference>` : The strings `members_source` and
+`center_source` are arbitrary keys that are used to reference the
+elements in `data_sources`.
+
 .. _convective precipitation: https://codes.ecmwf.int/grib/param-db/?id=143
 
 .. _ensemble forecasting: https://www.ecmwf.int/en/elibrary/75394-ensemble-forecasting
diff --git a/docs/building/sources/yaml/perturbations.yaml b/docs/building/sources/yaml/perturbations.yaml
index fe2da44c..6b4da333 100644
--- a/docs/building/sources/yaml/perturbations.yaml
+++ b/docs/building/sources/yaml/perturbations.yaml
@@ -1,5 +1,5 @@
 data_sources:
-  members:
+  members_source:
     class: ea
     expver: "0001"
     grid: 20.0/20.0
@@ -9,7 +9,7 @@ data_sources:
     stream: enda
     number: [1, 2, 3, 4, 5, 6, 7, 8, 9]
 
-  center:
+  center_source:
     class: ea
     expver: "0001"
     grid: 20.0/20.0
@@ -20,5 +20,5 @@ data_sources:
 
 input:
   perturbations:
-    center: ${data_sources.center}
-    members: ${data_sources.members}
+    center: ${data_sources.center_source}
+    members: ${data_sources.members_source}