Remove the else-clause because the conditions are no longer mutually exclusive.
diff --git a/Objects/setobject.c b/Objects/setobject.c
index da3b955..0db7e88 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -140,7 +140,7 @@
                 return set_lookkey(so, key, hash);
             }
         }
-        else if (entry->key == dummy && freeslot == NULL)
+        if (entry->key == dummy && freeslot == NULL)
             freeslot = entry;
     }
     return entry;