diff --git a/src/de/inetsoftware/jwebassembly/module/TypeManager.java b/src/de/inetsoftware/jwebassembly/module/TypeManager.java
index 95ecf3f..9d8a7c0 100644
--- a/src/de/inetsoftware/jwebassembly/module/TypeManager.java
+++ b/src/de/inetsoftware/jwebassembly/module/TypeManager.java
@@ -97,7 +97,7 @@ public class TypeManager {
             if( isFinish ) {
                 throw new WasmException( "Register needed type after scanning: " + name, -1 );
             }
-            type = new StructType( name );
+            type = new StructType( name, structTypes.size() );
             structTypes.put( name, type );
         }
         return type;
@@ -132,6 +132,8 @@ public class TypeManager {
 
         private final String           name;
 
+        private final int              classIndex;
+
         private int                    code = Integer.MAX_VALUE;
 
         private HashSet<String>        neededFields = new HashSet<>();
@@ -150,9 +152,12 @@ public class TypeManager {
          * 
          * @param name
          *            the Java class name
+         * @param classIndex
+         *            the running index of the class/type
          */
-        StructType( String name ) {
+        StructType( String name, int classIndex ) {
             this.name = name;
+            this.classIndex = classIndex;
         }
 
         /**
@@ -281,6 +286,15 @@ public class TypeManager {
             return name;
         }
 
+        /**
+         * The running index of the class/type for class meta data, instanceof and interface calls.
+         * 
+         * @return the unique index
+         */
+        public int getClassIndex() {
+            return classIndex;
+        }
+
         /**
          * Get the fields of this struct
          * @return the fields
diff --git a/src/de/inetsoftware/jwebassembly/module/WasmCallInstruction.java b/src/de/inetsoftware/jwebassembly/module/WasmCallInstruction.java
index 6a20cce..5e10953 100644
--- a/src/de/inetsoftware/jwebassembly/module/WasmCallInstruction.java
+++ b/src/de/inetsoftware/jwebassembly/module/WasmCallInstruction.java
@@ -37,6 +37,7 @@ class WasmCallInstruction extends WasmInstruction {
 
     private int               paramCount = -1;
 
+    @Nonnull
     private final TypeManager types;
 
     private final boolean     needThisParameter;
@@ -55,7 +56,7 @@ class WasmCallInstruction extends WasmInstruction {
      * @param needThisParameter
      *            true, if this function need additional to the parameter of the signature an extra "this" parameter
      */
-    WasmCallInstruction( FunctionName name, int javaCodePos, int lineNumber, TypeManager types, boolean needThisParameter ) {
+    WasmCallInstruction( FunctionName name, int javaCodePos, int lineNumber, @Nonnull TypeManager types, boolean needThisParameter ) {
         super( javaCodePos, lineNumber );
         this.name = name;
         this.types = types;
@@ -80,6 +81,14 @@ class WasmCallInstruction extends WasmInstruction {
         return name;
     }
 
+    /**
+     * Get the type manager.
+     * @return the manager
+     */
+    TypeManager getTypeManager() {
+        return types;
+    }
+
     /**
      * Mark the function as needed in the functions manager and replace the function name with a possible super name.
      * 
diff --git a/src/de/inetsoftware/jwebassembly/module/WasmCallInterfaceInstruction.java b/src/de/inetsoftware/jwebassembly/module/WasmCallInterfaceInstruction.java
index 221d5d6..4b0c4cb 100644
--- a/src/de/inetsoftware/jwebassembly/module/WasmCallInterfaceInstruction.java
+++ b/src/de/inetsoftware/jwebassembly/module/WasmCallInterfaceInstruction.java
@@ -21,6 +21,7 @@ import java.io.IOException;
 import javax.annotation.Nonnull;
 
 import de.inetsoftware.jwebassembly.WasmException;
+import de.inetsoftware.jwebassembly.module.TypeManager.StructType;
 
 /**
  * WasmInstruction for a function call.
@@ -58,6 +59,8 @@ class WasmCallInterfaceInstruction extends WasmCallInstruction {
      * {@inheritDoc}
      */
     public void writeTo( @Nonnull ModuleWriter writer ) throws IOException {
+        StructType type = getTypeManager().valueOf( getFunctionName().className );
+        int classIndex = type.getClassIndex();
         throw new WasmException( "Interface calls are not supported.", getLineNumber() );
     }
 }