diff --git a/bilby/gw/prior.py b/bilby/gw/prior.py
index 437b763bc172a8d913353da1530a59c22d140d36..ee286cdb220c03fc5324e38e0cbbd1cd2f06ab6a 100644
--- a/bilby/gw/prior.py
+++ b/bilby/gw/prior.py
@@ -413,7 +413,7 @@ class CorrelatedSecondaryMassPrior(Uniform):
         super(CorrelatedSecondaryMassPrior, self).__init__(minimum=minimum, maximum=maximum,
                                                            name=name, latex_label=latex_label,
                                                            unit=unit)
-        self.correlated_variables = dict(mass_1=None)
+        self.correlated_variables = ['mass_1']
 
     def sample(self, size=None, mass_1=None):
         if mass_1 is None: