diff --git a/src/de/inetsoftware/jwebassembly/module/JavaMethodWasmCodeBuilder.java b/src/de/inetsoftware/jwebassembly/module/JavaMethodWasmCodeBuilder.java
index e07ac26..d2d3980 100644
--- a/src/de/inetsoftware/jwebassembly/module/JavaMethodWasmCodeBuilder.java
+++ b/src/de/inetsoftware/jwebassembly/module/JavaMethodWasmCodeBuilder.java
@@ -224,6 +224,8 @@ class JavaMethodWasmCodeBuilder extends WasmCodeBuilder {
                         addBlockInstruction( WasmBlockOperator.DROP, null, codePos );
                         break;
                     case 89: // dup: duplicate the value on top of the stack
+                        addCallInstruction( new SyntheticMember( "de/inetsoftware/jwebassembly/module/NativeHelperCode", "dup_i32", "(I)II" ), codePos );
+                        break;
                     case 90: // dup_x1
                     case 91: // dup_x2
                     case 92: // dup2
diff --git a/src/de/inetsoftware/jwebassembly/module/NativeHelperCode.java b/src/de/inetsoftware/jwebassembly/module/NativeHelperCode.java
new file mode 100644
index 0000000..c583ad9
--- /dev/null
+++ b/src/de/inetsoftware/jwebassembly/module/NativeHelperCode.java
@@ -0,0 +1,25 @@
+/*
+ * Copyright 2018 Volker Berlin (i-net software)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package de.inetsoftware.jwebassembly.module;
+
+import de.inetsoftware.jwebassembly.api.annotation.WasmTextCode;
+
+public class NativeHelperCode {
+
+    @WasmTextCode( signature = "(I)II", value = "get_local 0 get_local 0 return" )
+    native static void dup_i32();
+
+ }
diff --git a/src/de/inetsoftware/jwebassembly/module/SyntheticMember.java b/src/de/inetsoftware/jwebassembly/module/SyntheticMember.java
new file mode 100644
index 0000000..73d6b0d
--- /dev/null
+++ b/src/de/inetsoftware/jwebassembly/module/SyntheticMember.java
@@ -0,0 +1,72 @@
+/*
+   Copyright 2018 Volker Berlin (i-net software)
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+*/
+package de.inetsoftware.jwebassembly.module;
+
+import de.inetsoftware.classparser.Member;
+
+/**
+ * A generated member that come not from the Java class parser.
+ * 
+ * @author Volker Berlin
+ */
+public class SyntheticMember implements Member {
+
+    
+    private final String className;
+    private final String name;
+    private final String type;
+
+    /**
+     * Create a new instance
+     * 
+     * @param className
+     *            the className
+     * @param name
+     *            the name
+     * @param type
+     *            the Java signature
+     */
+    SyntheticMember( String className, String name, String type ) {
+        this.className = className;
+        this.name = name;
+        this.type = type;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public String getName() {
+        return name;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public String getClassName() {
+        return className;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public String getType() {
+        return type;
+    }
+}