diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/debug/Frame-onStep-09.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/debug/Frame-onStep-09.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+// After an implicit toString call throws an exception, the calling frame's
+// onStep hook fires.
+
+var g = newGlobal();
+g.eval("var x = {toString: function () { debugger; log += 'x'; throw 'mud'; }};");
+
+var dbg = Debugger(g);
+dbg.onDebuggerStatement = function (frame) {
+    g.log += 'd';
+    frame.older.onStep = function () {
+        if (!g.log.match(/[sy]$/))
+            g.log += 's';
+    };
+};
+
+g.log = '';
+g.eval("try { x + ''; } catch (x) { }\n" +
+       "log += 'y';\n");
+assertEq(g.log, "dxsy");
+
+g.log = '';
+g.eval("try { '' + x; } catch (x) { }\n" +
+       "log += 'y';\n");
+assertEq(g.log, "dxsy");