diff --git a/jso/impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java b/jso/impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java
index 41fe6346a..6204f7b26 100644
--- a/jso/impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java
+++ b/jso/impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java
@@ -76,6 +76,8 @@ public class JSNativeGenerator implements Injector, DependencyPlugin, Generator
         String thisName = context.getParameterName(1);
         String methodName = context.getParameterName(2);
 
+        writer.append("if").ws().append("(").append(thisName).ws().append("===").ws().append("null)").ws()
+                .append("return null;").softNewLine();
         writer.append("var result").ws().append("=").ws().append("{};").softNewLine();
         writer.append("result[").append(methodName).append("]").ws().append("=").ws().append(thisName)
                 .append(";").softNewLine();