diff --git a/arviz/stats/stats.py b/arviz/stats/stats.py
index 8afc733d67..e4c78d3bcb 100644
--- a/arviz/stats/stats.py
+++ b/arviz/stats/stats.py
@@ -917,6 +917,7 @@ def psislw(log_weights, reff=1.0):
            ...: az.psislw(-log_likelihood, reff=0.8)
 
     """
+    log_weights = deepcopy(log_weights)
     if hasattr(log_weights, "__sample__"):
         n_samples = len(log_weights.__sample__)
         shape = [