diff --git a/compiler/transf.nim b/compiler/transf.nim
index d64276cfb..fc400c524 100644
--- a/compiler/transf.nim
+++ b/compiler/transf.nim
@@ -474,12 +474,14 @@ proc transformConv(c: PTransf, n: PNode): PTransNode =
 
 type
   TPutArgInto = enum
-    paDirectMapping, paFastAsgn, paVarAsgn
+    paDirectMapping, paFastAsgn, paVarAsgn, paComplexOpenarray
 
 proc putArgInto(arg: PNode, formal: PType): TPutArgInto =
   # This analyses how to treat the mapping "formal <-> arg" in an
   # inline context.
   if skipTypes(formal, abstractInst).kind in {tyOpenArray, tyVarargs}:
+    if arg.kind == nkStmtListExpr:
+      return paComplexOpenarray
     return paDirectMapping    # XXX really correct?
                               # what if ``arg`` has side-effects?
   case arg.kind
@@ -569,6 +571,14 @@ proc transformFor(c: PTransf, n: PNode): PTransNode =
       assert(skipTypes(formal.typ, abstractInst).kind == tyVar)
       idNodeTablePut(newC.mapping, formal, arg)
       # XXX BUG still not correct if the arg has a side effect!
+    of paComplexOpenarray:
+      let typ = newType(tySequence, formal.owner)
+      addSonSkipIntLit(typ, formal.typ.sons[0])
+      var temp = newTemp(c, typ, formal.info)
+      addVar(v, temp)
+      add(stmtList, newAsgnStmt(c, temp, arg.PTransNode))
+      idNodeTablePut(newC.mapping, formal, temp)
+
   var body = iter.getBody.copyTree
   pushInfoContext(n.info)
   # XXX optimize this somehow. But the check "c.inlining" is not correct:
diff --git a/tests/iter/tcomplex_openarray.nim b/tests/iter/tcomplex_openarray.nim
new file mode 100644
index 000000000..6fc191e90
--- /dev/null
+++ b/tests/iter/tcomplex_openarray.nim
@@ -0,0 +1,33 @@
+
+# bug #3221
+
+import algorithm, math, sequtils
+
+
+iterator permutations[T](ys: openarray[T]): seq[T] =
+  var
+    d = 1
+    c = newSeq[int](ys.len)
+    xs = newSeq[T](ys.len)
+  for i, y in ys: xs[i] = y
+  yield xs
+  block outer:
+    while true:
+      while d > 1:
+        dec d
+        c[d] = 0
+      while c[d] >= d:
+        inc d
+        if d >= ys.len: break outer
+      let i = if (d and 1) == 1: c[d] else: 0
+      swap xs[i], xs[d]
+      yield xs
+      inc c[d]
+
+proc dig_vectors(): void =
+  var v_nums: seq[int]
+  v_nums = newSeq[int](1)
+  for perm in permutations(toSeq(0 .. 1)):
+    v_nums[0] = 1
+
+dig_vectors()