diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index 541df65059..3c38851965 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -3612,55 +3612,6 @@ Parser<SyntaxParseHandler>::pushLetScope(HandleStaticBlockObject blockObj, StmtI
     return SyntaxParseHandler::NodeFailure;
 }
 
-/*
- * Parse a let block statement.
- * In both cases, bindings are not hoisted to the top of the enclosing block
- * and thus must be carefully injected between variables() and the let body.
- */
-template <typename ParseHandler>
-typename ParseHandler::Node
-Parser<ParseHandler>::deprecatedLetBlock()
-{
-    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_LET));
-
-    RootedStaticBlockObject blockObj(context, StaticBlockObject::create(context));
-    if (!blockObj)
-        return null();
-
-    uint32_t begin = pos().begin;
-
-    MUST_MATCH_TOKEN(TOK_LP, JSMSG_PAREN_BEFORE_LET);
-
-    Node vars = variables(PNK_LET, nullptr, blockObj, DontHoistVars);
-    if (!vars)
-        return null();
-
-    MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_AFTER_LET);
-
-    StmtInfoPC stmtInfo(context);
-    Node block = pushLetScope(blockObj, &stmtInfo);
-    if (!block)
-        return null();
-
-    MUST_MATCH_TOKEN(TOK_LC, JSMSG_CURLY_BEFORE_LET);
-
-    Node expr = statements();
-    if (!expr)
-        return null();
-    MUST_MATCH_TOKEN(TOK_RC, JSMSG_CURLY_AFTER_LET);
-
-    addTelemetry(JSCompartment::DeprecatedLetBlock);
-    if (!report(ParseWarning, pc->sc->strict, expr, JSMSG_DEPRECATED_LET_BLOCK))
-        return null();
-
-    handler.setLexicalScopeBody(block, expr);
-    PopStatementPC(tokenStream, pc);
-
-    TokenPos letPos(begin, pos().end);
-
-    return handler.newLetBlock(vars, block, letPos);
-}
-
 template <typename ParseHandler>
 static bool
 PushBlocklikeStatement(TokenStream& ts, StmtInfoPC* stmt, StmtType type,
@@ -4035,45 +3986,6 @@ Parser<SyntaxParseHandler>::lexicalDeclaration(bool)
     return SyntaxParseHandler::NodeFailure;
 }
 
-template <>
-ParseNode*
-Parser<FullParseHandler>::letDeclarationOrBlock()
-{
-    handler.disableSyntaxParser();
-
-    /* Check for a let statement. */
-    TokenKind tt;
-    if (!tokenStream.peekToken(&tt))
-        return null();
-    if (tt == TOK_LP) {
-        ParseNode* node = deprecatedLetBlock();
-        if (!node)
-            return nullptr;
-
-        MOZ_ASSERT(node->isKind(PNK_LETBLOCK));
-        MOZ_ASSERT(node->isArity(PN_BINARY));
-        return node;
-    }
-
-    ParseNode* decl = lexicalDeclaration(/* isConst = */ false);
-    if (!decl)
-        return nullptr;
-
-    // let-declarations at global scope are currently treated as plain old var.
-    // See bug 589199.
-    MOZ_ASSERT(decl->isKind(PNK_LET) || decl->isKind(PNK_VAR));
-    MOZ_ASSERT(decl->isArity(PN_LIST));
-    return decl;
-}
-
-template <>
-SyntaxParseHandler::Node
-Parser<SyntaxParseHandler>::letDeclarationOrBlock()
-{
-    JS_ALWAYS_FALSE(abortIfSyntaxParser());
-    return SyntaxParseHandler::NodeFailure;
-}
-
 template<typename ParseHandler>
 typename ParseHandler::Node
 Parser<ParseHandler>::importDeclaration()
@@ -5733,6 +5645,11 @@ Parser<ParseHandler>::statement(bool canHaveDirectives)
       case TOK_LC:
         return blockStatement();
 
+      case TOK_LET:
+        if (!abortIfSyntaxParser())
+            return null();
+        return lexicalDeclaration(/* isConst = */ false);
+        
       case TOK_CONST:
         if (!abortIfSyntaxParser())
             return null();
@@ -5751,8 +5668,6 @@ Parser<ParseHandler>::statement(bool canHaveDirectives)
         return pn;
       }
 
-      case TOK_LET:
-        return letDeclarationOrBlock();
       case TOK_IMPORT:
         return importDeclaration();
       case TOK_EXPORT:
diff --git a/js/src/frontend/Parser.h b/js/src/frontend/Parser.h
index 4723e764fd..825fdc7538 100644
--- a/js/src/frontend/Parser.h
+++ b/js/src/frontend/Parser.h
@@ -548,7 +548,6 @@ class Parser : private JS::AutoGCRooter, public StrictModeGetter
     Node debuggerStatement();
 
     Node lexicalDeclaration(bool isConst);
-    Node letDeclarationOrBlock();
     Node importDeclaration();
     Node exportDeclaration();
     Node expressionStatement(InvokedPrediction invoked = PredictUninvoked);
@@ -605,7 +604,6 @@ class Parser : private JS::AutoGCRooter, public StrictModeGetter
     Node generatorComprehension(uint32_t begin);
 
     bool argumentList(Node listNode, bool* isSpread);
-    Node deprecatedLetBlock();
     Node destructuringExpr(BindData<ParseHandler>* data, TokenKind tt);
     Node destructuringExprWithoutYield(BindData<ParseHandler>* data, TokenKind tt, unsigned msg);
 
diff --git a/js/src/js.msg b/js/src/js.msg
index 47ed2e45e1..4e64c4c0a5 100644
--- a/js/src/js.msg
+++ b/js/src/js.msg
@@ -227,7 +227,6 @@ MSG_DEF(JSMSG_CURLY_IN_COMPOUND,       0, JSEXN_SYNTAXERR, "missing } in compoun
 MSG_DEF(JSMSG_DECLARATION_AFTER_EXPORT,0, JSEXN_SYNTAXERR, "missing declaration after 'export' keyword")
 MSG_DEF(JSMSG_DECLARATION_AFTER_IMPORT,0, JSEXN_SYNTAXERR, "missing declaration after 'import' keyword")
 MSG_DEF(JSMSG_DEPRECATED_DELETE_OPERAND, 0, JSEXN_SYNTAXERR, "applying the 'delete' operator to an unqualified name is deprecated")
-MSG_DEF(JSMSG_DEPRECATED_LET_BLOCK,      0, JSEXN_NONE, "JavaScript 1.7's let blocks are deprecated")
 MSG_DEF(JSMSG_DEPRECATED_FOR_EACH,     0, JSEXN_NONE, "JavaScript 1.6's for-each-in loops are deprecated; consider using ES6 for-of instead")
 MSG_DEF(JSMSG_DEPRECATED_OCTAL,        0, JSEXN_SYNTAXERR, "octal literals and octal escape sequences are deprecated")
 MSG_DEF(JSMSG_DEPRECATED_PRAGMA,       1, JSEXN_NONE, "Using //@ to indicate {0} pragmas is deprecated. Use //# instead")
diff --git a/js/src/vm/Xdr.h b/js/src/vm/Xdr.h
index 8db07d3855..d0dd54f40c 100644
--- a/js/src/vm/Xdr.h
+++ b/js/src/vm/Xdr.h
@@ -29,11 +29,11 @@ namespace js {
  *
  *  https://developer.mozilla.org/en-US/docs/SpiderMonkey/Internals/Bytecode
  */
-static const uint32_t XDR_BYTECODE_VERSION_SUBTRAHEND = 248;
+static const uint32_t XDR_BYTECODE_VERSION_SUBTRAHEND = 249;
 static const uint32_t XDR_BYTECODE_VERSION =
     uint32_t(0xb973c0de - XDR_BYTECODE_VERSION_SUBTRAHEND);
 
-static_assert(JSErr_Limit == 368,
+static_assert(JSErr_Limit == 367,
               "GREETINGS, POTENTIAL SUBTRAHEND INCREMENTER! If you added or "
               "removed MSG_DEFs from js.msg, you should increment "
               "XDR_BYTECODE_VERSION_SUBTRAHEND and update this assertion's "