diff --git a/tupak/sampler.py b/tupak/sampler.py
index d7bf4dc554bd842dd68ba948892ac95fd45d78a2..66559f2e237d3828d81842414b94ad271d9ffbf4 100644
--- a/tupak/sampler.py
+++ b/tupak/sampler.py
@@ -456,7 +456,7 @@ def run_sampler(likelihood, priors=None, label='label', outdir='outdir',
         else:
             result.log_bayes_factor = result.logz - result.noise_logz
         result.injection_parameters = injection_parameters
-        result.fixed_parameter_keys = [key for key in priors if isinstance(key, prior.DeltaFunction)]
+        result.fixed_parameter_keys = sampler.fixed_parameter_keys
         result.priors = priors
         result.kwargs = sampler.kwargs
         result.samples_to_data_frame()