--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -1686,16 +1686,18 @@ DisplayName(JSContext* cx, unsigned argc
     JSFunction* fun = &args[0].toObject().as<JSFunction>();
     JSString* str = fun->displayAtom();
     args.rval().setString(str ? str : cx->runtime()->emptyString);
     return true;
 }
 
 class ShellAllocationMetadataBuilder : public AllocationMetadataBuilder {
   public:
+    ShellAllocationMetadataBuilder() : AllocationMetadataBuilder() { }
+
     virtual JSObject* build(JSContext *cx, HandleObject,
                             AutoEnterOOMUnsafeRegion& oomUnsafe) const override;
 
     static const ShellAllocationMetadataBuilder metadataBuilder;
 };
 
 JSObject*
 ShellAllocationMetadataBuilder::build(JSContext* cx, HandleObject,