diff --git a/js/src/jstracer.cpp b/js/src/jstracer.cpp
index cf9327baa13..9b52b8591c0 100644
--- a/js/src/jstracer.cpp
+++ b/js/src/jstracer.cpp
@@ -8286,13 +8286,21 @@ TraceRecorder::record_JSOP_TYPEOFEXPR()
 JS_REQUIRES_STACK bool
 TraceRecorder::record_JSOP_ENTERBLOCK()
 {
-    return false;
+    JSScript* script = cx->fp->script;
+    JSFrameRegs& regs = *cx->fp->regs;
+    JSObject* obj;
+    JS_GET_SCRIPT_OBJECT(script, GET_FULL_INDEX(0), obj);
+
+    LIns* void_ins = INS_CONST(JSVAL_TO_BOOLEAN(JSVAL_VOID));
+    for (int i = 0, n = OBJ_BLOCK_COUNT(cx, obj); i < n; i++)
+        stack(i, void_ins);
+    return true;
 }
 
 JS_REQUIRES_STACK bool
 TraceRecorder::record_JSOP_LEAVEBLOCK()
 {
-    return false;
+    return true;
 }
 
 JS_REQUIRES_STACK bool
@@ -8345,7 +8353,10 @@ TraceRecorder::record_JSOP_ENUMCONSTELEM()
 JS_REQUIRES_STACK bool
 TraceRecorder::record_JSOP_LEAVEBLOCKEXPR()
 {
-    return false;
+    LIns* v_ins = stack(-1);
+    int n = -1 - GET_UINT16(cx->fp->regs->pc);
+    stack(n, v_ins);
+    return true;
 }
 
 JS_REQUIRES_STACK bool