--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -6038,24 +6038,38 @@ Parser<ParseHandler>::assignExpr()
     // In such cases, we can avoid the full expression parsing route through
     // assignExpr(), condExpr1(), orExpr1(), unaryExpr(), memberExpr(), and
     // primaryExpr().
 
     TokenKind tt;
     if (!tokenStream.getToken(&tt, TokenStream::Operand))
         return null();
 
-    if (tt == TOK_NAME && tokenStream.nextTokenEndsExpr())
-        return identifierName();
-
-    if (tt == TOK_NUMBER && tokenStream.nextTokenEndsExpr())
-        return newNumber(tokenStream.currentToken());
-
-    if (tt == TOK_STRING && tokenStream.nextTokenEndsExpr())
-        return stringLiteral();
+    bool endsExpr;
+
+    if (tt == TOK_NAME) {
+        if (!tokenStream.nextTokenEndsExpr(&endsExpr))
+            return null();
+        if (endsExpr)
+            return identifierName();
+    }
+
+    if (tt == TOK_NUMBER) {
+        if (!tokenStream.nextTokenEndsExpr(&endsExpr))
+            return null();
+        if (endsExpr)
+            return newNumber(tokenStream.currentToken());
+    }
+
+    if (tt == TOK_STRING) {
+        if (!tokenStream.nextTokenEndsExpr(&endsExpr))
+            return null();
+        if (endsExpr)
+            return stringLiteral();
+    }
 
     if (tt == TOK_YIELD && (versionNumber() >= JSVERSION_1_7 || pc->isGenerator()))
         return yieldExpression();
 
     tokenStream.ungetToken();
 
     // Save the tokenizer state in case we find an arrow function and have to
     // rewind.

--- a/js/src/frontend/TokenStream.h
+++ b/js/src/frontend/TokenStream.h
@@ -483,21 +483,22 @@ class MOZ_STACK_CLASS TokenStream
             *matchedp = true;
         } else {
             *matchedp = false;
             ungetToken();
         }
         return true;
     }
 
-    bool nextTokenEndsExpr() {
+    bool nextTokenEndsExpr(bool *endsExpr) {
         TokenKind tt;
         if (!peekToken(&tt))
             return false;
-        return isExprEnding[tt];
+        *endsExpr = isExprEnding[tt];
+        return true;
     }
 
     class MOZ_STACK_CLASS Position {
       public:
         // The Token fields may contain pointers to atoms, so for correct
         // rooting we must ensure collection of atoms is disabled while objects
         // of this class are live.  Do this by requiring a dummy AutoKeepAtoms
         // reference in the constructor.