diff --git a/jso/impl/src/main/java/org/teavm/jso/impl/JSWrapperGenerator.java b/jso/impl/src/main/java/org/teavm/jso/impl/JSWrapperGenerator.java
index 4653f9179..0fe4a6758 100644
--- a/jso/impl/src/main/java/org/teavm/jso/impl/JSWrapperGenerator.java
+++ b/jso/impl/src/main/java/org/teavm/jso/impl/JSWrapperGenerator.java
@@ -40,7 +40,7 @@ public class JSWrapperGenerator implements Injector, DependencyPlugin {
                 break;
             case "isJava":
                 context.writeExpr(context.getArgument(0));
-                context.getWriter().append(" instanceof ").appendFunction("$rt_objcls").append("()");
+                context.getWriter().append(" instanceof ").append("$rt_objcls").append("()");
                 break;
         }
     }