diff --git a/src/cmd/compile/internal/gc/phi.go b/src/cmd/compile/internal/gc/phi.go
index 2f1d70a3ee4..0ba2de80e2c 100644
--- a/src/cmd/compile/internal/gc/phi.go
+++ b/src/cmd/compile/internal/gc/phi.go
@@ -437,6 +437,8 @@ type simplePhiState struct {
 }
 
 func (s *simplePhiState) insertPhis() {
+	reachable := ssa.ReachableBlocks(s.f)
+
 	// Find FwdRef ops.
 	for _, b := range s.f.Blocks {
 		for _, v := range b.Values {
@@ -459,12 +461,12 @@ loop:
 		s.fwdrefs = s.fwdrefs[:len(s.fwdrefs)-1]
 		b := v.Block
 		var_ := v.Aux.(*Node)
-		if len(b.Preds) == 0 {
-			if b == s.f.Entry {
-				// No variable should be live at entry.
-				s.s.Fatalf("Value live at entry. It shouldn't be. func %s, node %v, value %v", s.f.Name, var_, v)
-			}
-			// This block is dead; it has no predecessors and it is not the entry block.
+		if b == s.f.Entry {
+			// No variable should be live at entry.
+			s.s.Fatalf("Value live at entry. It shouldn't be. func %s, node %v, value %v", s.f.Name, var_, v)
+		}
+		if !reachable[b.ID] {
+			// This block is dead.
 			// It doesn't matter what we use here as long as it is well-formed.
 			v.Op = ssa.OpUnknown
 			v.Aux = nil
diff --git a/src/cmd/compile/internal/ssa/deadcode.go b/src/cmd/compile/internal/ssa/deadcode.go
index ce786a964b4..b24ecaa4c4b 100644
--- a/src/cmd/compile/internal/ssa/deadcode.go
+++ b/src/cmd/compile/internal/ssa/deadcode.go
@@ -6,13 +6,13 @@ package ssa
 
 // findlive returns the reachable blocks and live values in f.
 func findlive(f *Func) (reachable []bool, live []bool) {
-	reachable = reachableBlocks(f)
+	reachable = ReachableBlocks(f)
 	live = liveValues(f, reachable)
 	return
 }
 
-// reachableBlocks returns the reachable blocks in f.
-func reachableBlocks(f *Func) []bool {
+// ReachableBlocks returns the reachable blocks in f.
+func ReachableBlocks(f *Func) []bool {
 	reachable := make([]bool, f.NumBlocks())
 	reachable[f.Entry.ID] = true
 	p := []*Block{f.Entry} // stack-like worklist
@@ -106,7 +106,7 @@ func deadcode(f *Func) {
 	}
 
 	// Find reachable blocks.
-	reachable := reachableBlocks(f)
+	reachable := ReachableBlocks(f)
 
 	// Get rid of edges from dead to live code.
 	for _, b := range f.Blocks {
diff --git a/test/fixedbugs/issue19678.go b/test/fixedbugs/issue19678.go
new file mode 100644
index 00000000000..81ef331ee65
--- /dev/null
+++ b/test/fixedbugs/issue19678.go
@@ -0,0 +1,21 @@
+// compile
+
+// Copyright 2017 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.
+
+// Used to crash when compiling functions containing
+// forward refs in dead code.
+
+package p
+
+var f func(int)
+
+func g() {
+l1:
+	i := 0
+	goto l1
+l2:
+	f(i)
+	goto l2
+}