diff --git a/bilby/core/sampler/cpnest.py b/bilby/core/sampler/cpnest.py
index 0ac52c7ba1454d5c39949c03afc767842d6e9844..be46742558613695d8e2a6ce0fd8a6315b44f989 100644
--- a/bilby/core/sampler/cpnest.py
+++ b/bilby/core/sampler/cpnest.py
@@ -113,7 +113,7 @@ class Cpnest(NestedSampler):
                                      inplace=True)
         _, log_weights = compute_weights(np.array(self.result.nested_samples.log_likelihood),
                                          np.array(out.NS.state.nlive))
-        self.result.nested_samples.weights = np.exp(log_weights)
+        self.result.nested_samples['weights'] = np.exp(log_weights)
         self.result.log_evidence = out.NS.state.logZ
         self.result.log_evidence_err = np.sqrt(out.NS.state.info / out.NS.state.nlive)
         return self.result