src/jdk.jlink/share/classes/jdk/tools/jlink/internal/plugins/SystemModulesPlugin.java

@@ -769,11 +769,11 @@
                 mv.visitVarInsn(ALOAD, BUILDER_VAR);
 
                 if (md.isOpen()) {
                     setModuleBit("open", true);
                 }
-                if (md.isSynthetic()) {
+                if (md.modifiers().contains(ModuleDescriptor.Modifier.SYNTHETIC)) {
                     setModuleBit("synthetic", true);
                 }
             }
 
             /*