diff --git a/client/variablefieldswidget.cpp b/client/variablefieldswidget.cpp
index b4f1ad5..56d2a7c 100644
--- a/client/variablefieldswidget.cpp
+++ b/client/variablefieldswidget.cpp
@@ -338,7 +338,7 @@ void VariableFieldsWidget::loadProtocolFields(
     field->clear();
 
     field->addItem("Custom");
-    for (int i = 0; i < protocol->frameFieldCount(); i++) {
+    for (int i = 0; i < protocol->fieldCount(); i++) {
         if (!protocol->fieldFlags(i).testFlag(AbstractProtocol::FrameField))
             continue;
         QString name = protocol->fieldData(i, AbstractProtocol::FieldName)
diff --git a/common/abstractprotocol.cpp b/common/abstractprotocol.cpp
index d3583fa..40d8219 100644
--- a/common/abstractprotocol.cpp
+++ b/common/abstractprotocol.cpp
@@ -361,7 +361,8 @@ int AbstractProtocol::fieldFrameBitOffset(int index, int streamIndex) const
 {
     int ofs = 0;
 
-    if ((index < 0) || (index >= frameFieldCount()))
+    if ((index < 0) || (index >= fieldCount()) 
+            || !fieldFlags(index).testFlag(FrameField))
         return -1;
 
     // Lookup Cache; if not available calculate and cache (if enabled)