--- a/js/src/frontend/BinSource.cpp
+++ b/js/src/frontend/BinSource.cpp
@@ -150,17 +150,19 @@ private:
     bool readString(SimpleTokenReader* reader, MutableHandleAtom);
     bool readString(SimpleTokenReader* reader, MutableHandle<PropertyName*>);
     bool readBool(SimpleTokenReader* reader, Maybe<bool>&);
     bool readNumber(SimpleTokenReader* reader, Maybe<double>&);
 
     const Directives& currentDirectives() const {
         return this->currentDirectives_;
     }
-    ThisBinding thisBinding() const;
+    ThisBinding thisBinding() const {
+        return this->thisBinding_;
+    }
     const ReadOnlyCompileOptions& options() const {
         return this->options_;
     }
 
     // Names
 
     // --- GC.
 
@@ -214,16 +216,17 @@ private:
 
     JS_DECLARE_NEW_METHODS(new_, allocParseNode, inline)
 
 private:
     const ReadOnlyCompileOptions& options_;
     JSContext* cx;
     LifoAlloc& alloc;
     Directives currentDirectives_;
+    ThisBinding thisBinding_;
 
     // Needs access to AutoGCRooter.
     friend void TraceBinParser(JSTracer* trc, AutoGCRooter* parser);
 };
 
 class BinParseContext: public ParseContext {
 public:
     BinParseContext(ASTReader*, GlobalSharedContext*, Directives*);