diff --git a/bilby/core/prior/dict.py b/bilby/core/prior/dict.py
index c2aa966505254fdba9d9dd44b08c9f9e423ca69f..ca2eed960589fe5cb8d0bdfc05ca470fa00dfce5 100644
--- a/bilby/core/prior/dict.py
+++ b/bilby/core/prior/dict.py
@@ -364,6 +364,12 @@ class PriorDict(dict):
                     return sample
         else:
             needed = np.prod(size)
+            constraint_keys = list()
+            for ii, key in enumerate(keys[-1::-1]):
+                if isinstance(self[key], Constraint):
+                    constraint_keys.append(-ii - 1)
+            for ii in constraint_keys[-1::-1]:
+                del keys[ii]
             all_samples = {key: np.array([]) for key in keys}
             _first_key = list(all_samples.keys())[0]
             while len(all_samples[_first_key]) < needed: