diff --git a/mercurial/setdiscovery.py b/mercurial/setdiscovery.py
--- a/mercurial/setdiscovery.py
+++ b/mercurial/setdiscovery.py
@@ -99,9 +99,9 @@ def _limitsample(sample, desiredlen, ran
     """
     if len(sample) <= desiredlen:
         return sample
+    sample = list(sample)
     if randomize:
         return set(random.sample(sample, desiredlen))
-    sample = list(sample)
     sample.sort()
     return set(sample[:desiredlen])