diff --git a/Objects/setobject.c b/Objects/setobject.c
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -260,7 +260,8 @@
 {
     Py_ssize_t newsize;
     setentry *oldtable, *newtable, *entry;
-    Py_ssize_t i;
+    Py_ssize_t oldused = so->used;
+    Py_ssize_t oldfill = so->fill;
     int is_oldtable_malloced;
     setentry small_copy[PySet_MINSIZE];
 
@@ -314,16 +315,24 @@
     so->table = newtable;
     so->mask = newsize - 1;
     memset(newtable, 0, sizeof(setentry) * newsize);
-    i = so->used;
     so->used = 0;
     so->fill = 0;
 
     /* Copy the data over; this is refcount-neutral for active entries;
        dummy entries aren't copied over, of course */
-    for (entry = oldtable; i > 0; entry++) {
-        if (entry->key != NULL && entry->key != dummy) {
-            --i;
-            set_insert_clean(so, entry->key, entry->hash);
+    if (oldused == oldfill) {
+        for (entry = oldtable; oldused > 0; entry++) {
+            if (entry->key != NULL) {
+                oldused--;
+                set_insert_clean(so, entry->key, entry->hash);
+            }
+        }
+    } else {
+        for (entry = oldtable; oldused > 0; entry++) {
+            if (entry->key != NULL && entry->key != dummy) {
+                oldused--;
+                set_insert_clean(so, entry->key, entry->hash);
+            }
         }
     }