diff --git a/src/de/inetsoftware/jwebassembly/module/LocaleVariableManager.java b/src/de/inetsoftware/jwebassembly/module/LocaleVariableManager.java
index 13c139b..0684d86 100644
--- a/src/de/inetsoftware/jwebassembly/module/LocaleVariableManager.java
+++ b/src/de/inetsoftware/jwebassembly/module/LocaleVariableManager.java
@@ -359,6 +359,20 @@ class LocaleVariableManager {
         return var.idx;
     }
 
+    /**
+     * Expand code range for which the variable is valid
+     * 
+     * @param slot
+     *            the memory/slot index of the local variable
+     * @param javaCodePos
+     *            the new end code position in the Java method
+     */
+    void expandUse( int slot, int javaCodePos ) {
+        Variable var = variables[slot];
+        //TODO does we need to check for overlap with other slots?
+        var.endPos = Math.max( var.endPos, javaCodePos );
+    }
+
     /**
      * Get the WebAssembly variable index of the given Java Slot.
      * 
diff --git a/src/de/inetsoftware/jwebassembly/module/WasmCodeBuilder.java b/src/de/inetsoftware/jwebassembly/module/WasmCodeBuilder.java
index 6c5e58d..6dabb17 100644
--- a/src/de/inetsoftware/jwebassembly/module/WasmCodeBuilder.java
+++ b/src/de/inetsoftware/jwebassembly/module/WasmCodeBuilder.java
@@ -316,23 +316,28 @@ public abstract class WasmCodeBuilder {
     protected void addDupInstruction( int javaCodePos, int lineNumber ) {
         WasmInstruction instr = findInstructionThatPushValue( 1, javaCodePos );
         AnyType type = instr.getPushValueType();
-        int varIndex = -1;
+        int slot = -1;
         // if it is a GET to a local variable then we can use it
         if( instr.getType() == Type.Local ) {
             WasmLocalInstruction local1 = (WasmLocalInstruction)instr;
-            if( local1.getOperator() == VariableOperator.get ) {
-                varIndex = local1.getIndex();
+            switch( local1.getOperator() ) {
+                case get:
+                case tee:
+                    slot = local1.getSlot();
+                    break;
+                default:
             }
         }
         //alternate we need to create a new locale variable
-        if( varIndex < 0 ) {
-            varIndex = getTempVariable( type, javaCodePos, javaCodePos + 1 );
-            instructions.add( new WasmLoadStoreInstruction( VariableOperator.tee, varIndex, localVariables, javaCodePos, lineNumber ) );
-            instructions.add( new WasmLoadStoreInstruction( VariableOperator.get, varIndex, localVariables, javaCodePos, lineNumber ) );
+        if( slot < 0 ) {
+            slot = getTempVariable( type, javaCodePos, javaCodePos + 1 );
+            instructions.add( new WasmLoadStoreInstruction( VariableOperator.tee, slot, localVariables, javaCodePos, lineNumber ) );
+            instructions.add( new WasmLoadStoreInstruction( VariableOperator.get, slot, localVariables, javaCodePos, lineNumber ) );
             // an alternative solution can be a function call with multiple return values but this seems to be slower
             // new SyntheticFunctionName( "dup" + storeType, "local.get 0 local.get 0 return", storeType, null, storeType, storeType ), codePos, lineNumber )
         } else {
-            instructions.add( new WasmLocalInstruction( VariableOperator.get, varIndex, localVariables, javaCodePos, lineNumber ) );
+            instructions.add( new WasmLoadStoreInstruction( VariableOperator.get, slot, localVariables, javaCodePos, lineNumber ) );
+            localVariables.expandUse( slot, javaCodePos );
         }
     }
 
diff --git a/src/de/inetsoftware/jwebassembly/module/WasmLocalInstruction.java b/src/de/inetsoftware/jwebassembly/module/WasmLocalInstruction.java
index df4c51f..e2fb3bf 100644
--- a/src/de/inetsoftware/jwebassembly/module/WasmLocalInstruction.java
+++ b/src/de/inetsoftware/jwebassembly/module/WasmLocalInstruction.java
@@ -90,6 +90,16 @@ class WasmLocalInstruction extends WasmInstruction {
         this.op = op;
     }
 
+    /**
+     * Get the slot of the locals
+     * 
+     * @return the Java slot for the variable
+     */
+    @Nonnegative
+    int getSlot() {
+        return idx;
+    }
+
     /**
      * Get the number of the locals
      *