diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 55ab8ce2..eee3051 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -4536,6 +4536,9 @@
 // where v should be spilled.
 func autoVar(v *ssa.Value) (*Node, int64) {
 	loc := v.Block.Func.RegAlloc[v.ID].(ssa.LocalSlot)
+	if v.Type.Size() > loc.Type.Size() {
+		v.Fatalf("spill/restore type %s doesn't fit in slot type %s", v.Type, loc.Type)
+	}
 	return loc.N.(*Node), loc.Off
 }
 
diff --git a/src/cmd/compile/internal/gc/ssa_test.go b/src/cmd/compile/internal/gc/ssa_test.go
index 74fa847..d0c44b5 100644
--- a/src/cmd/compile/internal/gc/ssa_test.go
+++ b/src/cmd/compile/internal/gc/ssa_test.go
@@ -95,3 +95,5 @@
 func TestCopy(t *testing.T) { runTest(t, "copy_ssa.go") }
 
 func TestUnsafe(t *testing.T) { runTest(t, "unsafe_ssa.go") }
+
+func TestPhi(t *testing.T) { runTest(t, "phi_ssa.go") }
diff --git a/src/cmd/compile/internal/gc/testdata/phi_ssa.go b/src/cmd/compile/internal/gc/testdata/phi_ssa.go
new file mode 100644
index 0000000..e855070
--- /dev/null
+++ b/src/cmd/compile/internal/gc/testdata/phi_ssa.go
@@ -0,0 +1,103 @@
+// 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 main
+
+// Test to make sure spills of cast-shortened values
+// don't end up spilling the pre-shortened size instead
+// of the post-shortened size.
+
+import (
+	"fmt"
+	"runtime"
+)
+
+// unfoldable true
+var true_ = true
+
+var data1 [26]int32
+var data2 [26]int64
+
+func init() {
+	for i := 0; i < 26; i++ {
+		// If we spill all 8 bytes of this datum, the 1 in the high-order 4 bytes
+		// will overwrite some other variable in the stack frame.
+		data2[i] = 0x100000000
+	}
+}
+
+func foo() int32 {
+	var a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z int32
+	if true_ {
+		a = data1[0]
+		b = data1[1]
+		c = data1[2]
+		d = data1[3]
+		e = data1[4]
+		f = data1[5]
+		g = data1[6]
+		h = data1[7]
+		i = data1[8]
+		j = data1[9]
+		k = data1[10]
+		l = data1[11]
+		m = data1[12]
+		n = data1[13]
+		o = data1[14]
+		p = data1[15]
+		q = data1[16]
+		r = data1[17]
+		s = data1[18]
+		t = data1[19]
+		u = data1[20]
+		v = data1[21]
+		w = data1[22]
+		x = data1[23]
+		y = data1[24]
+		z = data1[25]
+	} else {
+		a = int32(data2[0])
+		b = int32(data2[1])
+		c = int32(data2[2])
+		d = int32(data2[3])
+		e = int32(data2[4])
+		f = int32(data2[5])
+		g = int32(data2[6])
+		h = int32(data2[7])
+		i = int32(data2[8])
+		j = int32(data2[9])
+		k = int32(data2[10])
+		l = int32(data2[11])
+		m = int32(data2[12])
+		n = int32(data2[13])
+		o = int32(data2[14])
+		p = int32(data2[15])
+		q = int32(data2[16])
+		r = int32(data2[17])
+		s = int32(data2[18])
+		t = int32(data2[19])
+		u = int32(data2[20])
+		v = int32(data2[21])
+		w = int32(data2[22])
+		x = int32(data2[23])
+		y = int32(data2[24])
+		z = int32(data2[25])
+	}
+	// Lots of phis of the form phi(int32,int64) of type int32 happen here.
+	// Some will be stack phis.  For those stack phis, make sure the spill
+	// of the second argument uses the phi's width (4 bytes), not its width
+	// (8 bytes).  Otherwise, a random stack slot gets clobbered.
+
+	runtime.Gosched()
+	return a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z
+}
+
+func main() {
+	want := int32(0)
+	got := foo()
+	if got != want {
+		fmt.Printf("want %d, got %d\n", want, got)
+		panic("bad")
+	}
+}
diff --git a/src/cmd/compile/internal/ssa/regalloc.go b/src/cmd/compile/internal/ssa/regalloc.go
index d7c4674..27deeba 100644
--- a/src/cmd/compile/internal/ssa/regalloc.go
+++ b/src/cmd/compile/internal/ssa/regalloc.go
@@ -1223,7 +1223,10 @@
 			r := e.findRegFor(v.Type)
 			x = v.copyInto(e.p)
 			e.set(r, vid, x, false)
-			x = e.p.NewValue1(x.Line, OpStoreReg, x.Type, x)
+			// Make sure we spill with the size of the slot, not the
+			// size of x (which might be wider due to our dropping
+			// of narrowing conversions).
+			x = e.p.NewValue1(x.Line, OpStoreReg, loc.(LocalSlot).Type, x)
 		}
 	} else {
 		// Emit move from src to dst.
@@ -1232,7 +1235,7 @@
 			if dstReg {
 				x = e.p.NewValue1(c.Line, OpCopy, c.Type, c)
 			} else {
-				x = e.p.NewValue1(c.Line, OpStoreReg, c.Type, c)
+				x = e.p.NewValue1(c.Line, OpStoreReg, loc.(LocalSlot).Type, c)
 			}
 		} else {
 			if dstReg {
@@ -1255,7 +1258,7 @@
 				r := e.findRegFor(c.Type)
 				t := e.p.NewValue1(c.Line, OpLoadReg, c.Type, c)
 				e.set(r, vid, t, false)
-				x = e.p.NewValue1(c.Line, OpStoreReg, c.Type, t)
+				x = e.p.NewValue1(c.Line, OpStoreReg, loc.(LocalSlot).Type, t)
 			}
 		}
 	}