diff --git a/openquake/calculators/hazard/event_based/core_next.py b/openquake/calculators/hazard/event_based/core_next.py
index <HASH>..<HASH> 100644
--- a/openquake/calculators/hazard/event_based/core_next.py
+++ b/openquake/calculators/hazard/event_based/core_next.py
@@ -267,8 +267,8 @@ def _get_correl_model(hc):
         '%sCorrelationModel' % hc.ground_motion_correlation_model,
         None)
     if correl_model_cls is None:
-        raise RuntimeError("Unknown correlation model: '%s'"
-                           % hc.ground_motion_correlation_model)
+        # There's no correlation model for this calculation.
+        return None
 
     return correl_model_cls(**hc.ground_motion_correlation_params)
calcs/hazard/event_based/core_next:

Allow the user to run calculations without a correlation model.