diff --git a/src/de/inetsoftware/jwebassembly/binary/BinaryModuleWriter.java b/src/de/inetsoftware/jwebassembly/binary/BinaryModuleWriter.java
index 7d8ea52..83c9956 100644
--- a/src/de/inetsoftware/jwebassembly/binary/BinaryModuleWriter.java
+++ b/src/de/inetsoftware/jwebassembly/binary/BinaryModuleWriter.java
@@ -478,7 +478,7 @@ public class BinaryModuleWriter extends ModuleWriter implements InstructionOpcod
      * {@inheritDoc}
      */
     @Override
-    public void prepareFinish() {
+    protected void prepareFinish() {
         // initialize the function index IDs
         // https://github.com/WebAssembly/design/blob/master/Modules.md#function-index-space
         int id = 0;
diff --git a/src/de/inetsoftware/jwebassembly/module/ModuleGenerator.java b/src/de/inetsoftware/jwebassembly/module/ModuleGenerator.java
index de45092..3e808f4 100644
--- a/src/de/inetsoftware/jwebassembly/module/ModuleGenerator.java
+++ b/src/de/inetsoftware/jwebassembly/module/ModuleGenerator.java
@@ -150,8 +150,6 @@ public class ModuleGenerator {
      *             if any I/O error occur
      */
     public void prepareFinish() throws IOException {
-        writer.prepareFinish();
-
         // scan all methods that should be write to build optimize structures
         FunctionName next;
         NEXT:
@@ -159,6 +157,7 @@ public class ModuleGenerator {
             ClassFile classFile = ClassFile.get( next.className, libraries );
             if( classFile == null ) {
                 if( next instanceof SyntheticFunctionName ) {
+                    writeMethodSignature( next, true, null );
                     scanMethod( ((SyntheticFunctionName)next).getCodeBuilder( watParser ) );
                     functions.markAsScanned( next );
                 }
@@ -167,6 +166,7 @@ public class ModuleGenerator {
                     try {
                         FunctionName name = new FunctionName( method );
                         if( functions.needToScan( name ) ) {
+                            writeMethodSignature( name, method.isStatic(), null );
                             scanMethod( createInstructions( method ) );
                             functions.markAsScanned( name );
                         }
@@ -196,6 +196,7 @@ public class ModuleGenerator {
         functions.prepareFinish();
 
         types.prepareFinish( writer, functions, libraries );
+        writer.prepareFinish();
     }
 
     /**
diff --git a/src/de/inetsoftware/jwebassembly/module/ModuleWriter.java b/src/de/inetsoftware/jwebassembly/module/ModuleWriter.java
index 9fc29cc..f5ec237 100644
--- a/src/de/inetsoftware/jwebassembly/module/ModuleWriter.java
+++ b/src/de/inetsoftware/jwebassembly/module/ModuleWriter.java
@@ -42,9 +42,7 @@ public abstract class ModuleWriter implements Closeable {
      * Finish the prepare after all classes/methods are prepare. This must be call before we can start with write the
      * first method.
      */
-    public void prepareFinish() {
-
-    }
+    protected abstract void prepareFinish();
 
     /**
      * Write a type/struct.
diff --git a/src/de/inetsoftware/jwebassembly/text/TextModuleWriter.java b/src/de/inetsoftware/jwebassembly/text/TextModuleWriter.java
index fc9c0bf..246de15 100644
--- a/src/de/inetsoftware/jwebassembly/text/TextModuleWriter.java
+++ b/src/de/inetsoftware/jwebassembly/text/TextModuleWriter.java
@@ -71,6 +71,8 @@ public class TextModuleWriter extends ModuleWriter {
 
     private boolean                     isImport;
 
+    private boolean                     isPrepared;
+
     private HashSet<String>             globals          = new HashSet<>();
 
     private boolean                     useExceptions;
@@ -187,6 +189,14 @@ public class TextModuleWriter extends ModuleWriter {
         }
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    protected void prepareFinish() {
+        isPrepared = true;
+    }
+
     /**
      * {@inheritDoc}
      */
@@ -273,6 +283,9 @@ public class TextModuleWriter extends ModuleWriter {
             writeTypeName( typeOutput, valueType );
             typeOutput.append( ')' );
         }
+        if( !isPrepared ) {
+            return;
+        }
         methodOutput.append( '(' ).append( kind );
         if( debugNames ) { 
             if( name != null ) {
@@ -563,10 +576,13 @@ public class TextModuleWriter extends ModuleWriter {
     protected void writeVirtualFunctionCall( FunctionName name, AnyType type, int virtualFunctionIdx ) throws IOException {
         callIndirect = true;
         newline( methodOutput );
-        methodOutput.append( "struct.get $" ).append( normalizeName( type.toString() ) ).append( " 0 ;;vtable" ); // vtable is ever on position 0
+        methodOutput.append( "struct.get " ).append( normalizeName( type.toString() ) ).append( " 0 ;;vtable" ); // vtable is ever on position 0
         newline( methodOutput );
         methodOutput.append( "i32.load offset=" ).append( virtualFunctionIdx * 4 ); // use default alignment
         newline( methodOutput );
+        if(spiderMonkey)
+            methodOutput.append( "call_indirect $t" ).append( functions.get( name.signatureName ) ); // https://bugzilla.mozilla.org/show_bug.cgi?id=1556779
+        else
         methodOutput.append( "call_indirect (type $t" ).append( functions.get( name.signatureName ) ).append( ')' );
     }