diff --git a/src/ert/run_models/base_run_model.py b/src/ert/run_models/base_run_model.py
index ef4c1737fc9..417222503b7 100644
--- a/src/ert/run_models/base_run_model.py
+++ b/src/ert/run_models/base_run_model.py
@@ -738,7 +738,7 @@ def update(
                 analysis_config=self.update_settings,
                 es_settings=self.es_settings,
                 parameters=prior.experiment.update_parameters,
-                observations=prior.experiment.observations.keys(),
+                observations=prior.experiment.observation_keys,
                 global_scaling=weight,
                 rng=self.rng,
                 progress_callback=functools.partial(