Version 5.1.281.23 (cherry-pick)

src/parsing/parser-base.h

Index: src/parsing/parser-base.h
diff --git a/src/parsing/parser-base.h b/src/parsing/parser-base.h
index 8664586cf66e258c4fcfe77fb031beb3de9ec6d0..cdfbe7e0f32e7af404f78abfb1bc6c726ea5596c 100644
--- a/src/parsing/parser-base.h
+++ b/src/parsing/parser-base.h
@@ -2872,6 +2872,10 @@ ParserBase<Traits>::ParseArrowFunctionLiteral(
       body->Add(factory()->NewReturnStatement(expression, pos), zone());
       materialized_literal_count = function_state.materialized_literal_count();
       expected_property_count = function_state.expected_property_count();
+      // ES6 14.6.1 Static Semantics: IsInTailPosition
+      if (allow_tailcalls() && !is_sloppy(language_mode())) {
+        this->MarkTailPosition(expression);
+      }
     }
     super_loc = function_state.super_location();