diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py
--- a/Lib/test/test_peepholer.py
+++ b/Lib/test/test_peepholer.py
@@ -267,11 +267,23 @@
         asm = disassemble(f)
         self.assertNotIn('BINARY_ADD', asm)
 
+class TestBuglets(unittest.TestCase):
+
+    def test_bug_11510(self):
+        # folded constant set optimization was commingled with the tuple
+        # unpacking optimization which would fail if the set had duplicate
+        # elements so that the set length was unexpected
+        def f():
+            x, y = {1, 1}
+            return x, y
+        with self.assertRaises(ValueError):
+            f()
+
 
 def test_main(verbose=None):
     import sys
     from test import support
-    test_classes = (TestTranforms,)
+    test_classes = (TestTranforms, TestBuglets)
     support.run_unittest(*test_classes)
 
     # verify reference counting
diff --git a/Python/peephole.c b/Python/peephole.c
--- a/Python/peephole.c
+++ b/Python/peephole.c
@@ -473,6 +473,8 @@
                     cumlc = 1;
                     break;
                 }
+                if (opcode == BUILD_SET)
+                    continue;
                 if (codestr[i+3] != UNPACK_SEQUENCE  ||
                     !ISBASICBLOCK(blocks,i,6) ||
                     j != GETARG(codestr, i+3))