diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index 0bb2badde5..65e51e4d1f 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -778,6 +778,7 @@ scanblock(Workbuf *wbuf, bool keepworking)
 	void *obj;
 	Type *t;
 	Slice *sliceptr;
+	String *stringptr;
 	Frame *stack_ptr, stack_top, stack[GC_STACK_CAPACITY+4];
 	BufferList *scanbuffers;
 	Scanbuf sbuf;
@@ -948,8 +949,11 @@ scanblock(Workbuf *wbuf, bool keepworking)
 			break;
 
 		case GC_STRING:
-			obj = *(void**)(stack_top.b + pc[1]);
-			markonly(obj);
+			stringptr = (String*)(stack_top.b + pc[1]);
+			if(stringptr->len != 0) {
+				obj = stringptr->str;
+				markonly(obj);
+			}
 			pc += 2;
 			continue;
 
diff --git a/test/gcstring.go b/test/gcstring.go
new file mode 100644
index 0000000000..627a426455
--- /dev/null
+++ b/test/gcstring.go
@@ -0,0 +1,48 @@
+// run
+
+// Copyright 2014 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.
+
+// Test that s[len(s):] - which can point past the end of the allocated block -
+// does not confuse the garbage collector.
+
+package main
+
+import (
+	"runtime"
+	"time"
+)
+
+type T struct {
+	ptr **int
+	pad [120]byte
+}
+
+var things []interface{}
+
+func main() {
+	setup()
+	runtime.GC()
+	runtime.GC()
+	time.Sleep(10*time.Millisecond)
+	runtime.GC()
+	runtime.GC()
+	time.Sleep(10*time.Millisecond)
+}
+
+func setup() {
+	var Ts []interface{}
+	buf := make([]byte, 128)
+	
+	for i := 0; i < 10000; i++ {
+		s := string(buf)
+		t := &T{ptr: new(*int)}
+		runtime.SetFinalizer(t.ptr, func(**int) { panic("*int freed too early") })
+		Ts = append(Ts, t)
+		things = append(things, s[len(s):])
+	}
+	
+	things = append(things, Ts...)
+}
+