diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index b6b858c0d9..2e4caca155 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -156,6 +156,8 @@ var Debug_typeassert int
 
 var localpkg *Pkg // package being compiled
 
+var autopkg *Pkg // fake package for allocating auto variables
+
 var importpkg *Pkg // package being imported
 
 var itabpkg *Pkg // fake pkg for itab entries
diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index 8ad3300dbe..b4df7ed20f 100644
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -108,6 +108,8 @@ func Main() {
 
 	localpkg = mkpkg("")
 	localpkg.Prefix = "\"\""
+	autopkg = mkpkg("")
+	autopkg.Prefix = "\"\""
 
 	// pseudo-package, for scoping
 	builtinpkg = mkpkg("go.builtin")
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index b604044cb7..d27ac4392f 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -4378,7 +4378,7 @@ func (e *ssaExport) SplitStruct(name ssa.LocalSlot, i int) ssa.LocalSlot {
 // namedAuto returns a new AUTO variable with the given name and type.
 func (e *ssaExport) namedAuto(name string, typ ssa.Type) ssa.GCNode {
 	t := typ.(*Type)
-	s := Lookup(name)
+	s := &Sym{Name: name, Pkg: autopkg}
 	n := Nod(ONAME, nil, nil)
 	s.Def = n
 	s.Def.Used = true
diff --git a/test/fixedbugs/issue15961.go b/test/fixedbugs/issue15961.go
new file mode 100644
index 0000000000..db3d662378
--- /dev/null
+++ b/test/fixedbugs/issue15961.go
@@ -0,0 +1,21 @@
+// compile
+
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package y
+
+type symSet []int
+
+//go:noinline
+func (s symSet) len() (r int) {
+	return 0
+}
+
+func f(m map[int]symSet) {
+	var symSet []int
+	for _, x := range symSet {
+		m[x] = nil
+	}
+}