diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/debug/Debugger-debuggees-10.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/debug/Debugger-debuggees-10.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,18 @@
+// Allow diamonds in the graph of the compartment "debugs" relation.
+var program = newGlobal();
+var d1 = newGlobal();
+d1.top = this;
+var d2 = newGlobal();
+d2.top = this;
+var dbg = new Debugger(d1, d2);
+d1.eval("var dbg = new Debugger(top.program)");
+d2.eval("var dbg = new Debugger(top.program)");
+
+// mess with the edges a little bit -- all this should be fine, no cycles
+d1.dbg.removeDebuggee(program);
+d1.dbg.addDebuggee(program);
+dbg.addDebuggee(program);
+d1.dbg.addDebuggee(d2);
+dbg.removeDebuggee(d2);
+dbg.addDebuggee(d2);
+