diff --git a/js/src/jsemit.c b/js/src/jsemit.c
index e80834658679..ae0dc5118037 100644
--- a/js/src/jsemit.c
+++ b/js/src/jsemit.c
@@ -4340,9 +4340,15 @@ js_EmitTree(JSContext *cx, JSCodeGenerator *cg, JSParseNode *pn)
       case TOK_UNARYOP:
         /* Unary op, including unary +/-. */
         pn2 = pn->pn_kid;
+        op = pn->pn_op;
+        if (op == JSOP_TYPEOF) {
+            for (pn3 = pn2; pn3->pn_type == TOK_RP; pn3 = pn3->pn_kid)
+                continue;
+            if (pn3->pn_type != TOK_NAME)
+                op = JSOP_TYPEOFEXPR;
+        }
         if (!js_EmitTree(cx, cg, pn2))
             return JS_FALSE;
-        op = pn->pn_op;
 #if JS_HAS_XML_SUPPORT
         if (op == JSOP_XMLNAME &&
             js_NewSrcNote2(cx, cg, SRC_PCBASE,
diff --git a/js/src/jsinterp.c b/js/src/jsinterp.c
index 3de62680f283..055f80a592f1 100644
--- a/js/src/jsinterp.c
+++ b/js/src/jsinterp.c
@@ -3434,6 +3434,7 @@ interrupt:
             STORE_OPND(-1, rval);
           END_CASE(JSOP_DELELEM)
 
+          BEGIN_CASE(JSOP_TYPEOFEXPR)
           BEGIN_CASE(JSOP_TYPEOF)
             rval = FETCH_OPND(-1);
             SAVE_SP_AND_PC(fp);
diff --git a/js/src/jsopcode.c b/js/src/jsopcode.c
index 14f212371268..c2c9cfc5f276 100644
--- a/js/src/jsopcode.c
+++ b/js/src/jsopcode.c
@@ -1806,6 +1806,7 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
                 break;
 #endif
 
+              case JSOP_TYPEOFEXPR:
               case JSOP_TYPEOF:
               case JSOP_VOID:
                 rval = POP_STR();
diff --git a/js/src/jsopcode.tbl b/js/src/jsopcode.tbl
index 2bf114fe31f5..d8714d4ab767 100644
--- a/js/src/jsopcode.tbl
+++ b/js/src/jsopcode.tbl
@@ -405,3 +405,4 @@ OPDEF(JSOP_STOP,          195,"stop",        NULL,    1,  0,  0,  0,  JOF_BYTE)
  */
 OPDEF(JSOP_GETXPROP,      196,"getxprop",    NULL,    3,  1,  1, 12,  JOF_CONST|JOF_PROP)
 OPDEF(JSOP_GETXELEM,      197,"getxelem",    NULL,    1,  2,  1, 12,  JOF_BYTE |JOF_ELEM|JOF_LEFTASSOC)
+OPDEF(JSOP_TYPEOFEXPR,    198, js_typeof_str,NULL,    1,  1,  1, 10,  JOF_BYTE|JOF_DETECTING)