diff --git a/python/gui/qgsfieldcombobox.sip b/python/gui/qgsfieldcombobox.sip
index 2a0b3c90b27..10c214e915c 100644
--- a/python/gui/qgsfieldcombobox.sip
+++ b/python/gui/qgsfieldcombobox.sip
@@ -24,6 +24,8 @@ class QgsFieldComboBox : QComboBox
 
     //! Returns the currently used layer
     QgsVectorLayer* layer();
+    
+    void changeEvent( QEvent* event );
 
   signals:
     //! the signal is emitted when the currently selected field changes
diff --git a/python/gui/qgsfieldexpressionwidget.sip b/python/gui/qgsfieldexpressionwidget.sip
index a4fe77b17a8..9d9e924e47b 100644
--- a/python/gui/qgsfieldexpressionwidget.sip
+++ b/python/gui/qgsfieldexpressionwidget.sip
@@ -20,11 +20,14 @@ class QgsFieldExpressionWidget : QWidget
     /**
      * @brief currentField returns the currently selected field or expression if allowed
      * @param isExpression determines if the string returned is the name of a field or an expression
+     * @param isValid determines if the expression (or field) returned is valid
      */
-    QString currentField( bool *isExpression = 0 );
+    QString currentField( bool *isExpression = 0, bool *isValid = 0 );
 
     //! Returns the currently used layer
     QgsVectorLayer* layer();
+    
+    void changeEvent( QEvent* event );
 
   signals:
     //! the signal is emitted when the currently selected field changes
diff --git a/src/gui/qgsfieldexpressionwidget.cpp b/src/gui/qgsfieldexpressionwidget.cpp
index 34283f92fc9..4071a377f33 100644
--- a/src/gui/qgsfieldexpressionwidget.cpp
+++ b/src/gui/qgsfieldexpressionwidget.cpp
@@ -44,7 +44,7 @@ QgsFieldExpressionWidget::QgsFieldExpressionWidget( QWidget *parent )
   layout->addWidget( mButton );
 
   connect( mCombo->lineEdit(), SIGNAL( textEdited( QString ) ), this, SLOT( expressionEdited( QString ) ) );
-  connect( mCombo, SIGNAL( currentIndexChanged( int ) ), this, SLOT( indexChanged( int ) ) );
+  connect( mCombo, SIGNAL( activated( int ) ), this, SLOT( currentFieldChanged( int ) ) );
   connect( mButton, SIGNAL( clicked() ), this, SLOT( editExpression() ) );
 }
 
@@ -58,15 +58,18 @@ void QgsFieldExpressionWidget::setGeomCalculator( const QgsDistanceArea &da )
   mDa = QSharedPointer<const QgsDistanceArea>( new QgsDistanceArea( da ) );
 }
 
-QString QgsFieldExpressionWidget::currentField( bool *isExpression )
+QString QgsFieldExpressionWidget::currentField( bool *isExpression , bool *isValid )
 {
   if ( isExpression )
   {
     *isExpression = false;
   }
+  if ( isValid )
+  {
+    *isValid = true;
+  }
 
   int i = mCombo->currentIndex();
-
   const QModelIndex index = mFieldModel->index( i, 0 );
   if ( !index.isValid() )
   {
@@ -77,6 +80,10 @@ QString QgsFieldExpressionWidget::currentField( bool *isExpression )
   {
     *isExpression = mFieldModel->data( index, QgsFieldModel::IsExpressionRole ).toBool();
   }
+  if ( isValid )
+  {
+    *isValid = mFieldModel->data( index, QgsFieldModel::ExpressionValidityRole ).toBool();
+  }
   QString expression = mFieldModel->data( index, QgsFieldModel::ExpressionRole ).toString();
   return expression;
 }
@@ -100,7 +107,7 @@ void QgsFieldExpressionWidget::setLayer( QgsVectorLayer *layer )
   mFieldModel->setLayer( layer );
 }
 
-void QgsFieldExpressionWidget::setField( QString fieldName )
+void QgsFieldExpressionWidget::setField( const QString fieldName )
 {
   if ( fieldName.isEmpty() )
     return;
@@ -112,6 +119,8 @@ void QgsFieldExpressionWidget::setField( QString fieldName )
     idx = mFieldModel->setExpression( fieldName );
   }
   mCombo->setCurrentIndex( idx.row() );
+
+  currentFieldChanged();
 }
 
 void QgsFieldExpressionWidget::editExpression()
@@ -136,39 +145,57 @@ void QgsFieldExpressionWidget::editExpression()
   }
 }
 
-void QgsFieldExpressionWidget::expressionEdited( QString expression )
+void QgsFieldExpressionWidget::expressionEdited( const QString expression )
 {
-  mFieldModel->removeExpression();
-  setField( expression );
+  QModelIndex idx = mFieldModel->setExpression( expression );
+  mCombo->setCurrentIndex( idx.row() );
+  currentFieldChanged();
 }
 
-void QgsFieldExpressionWidget::indexChanged( int i )
+void QgsFieldExpressionWidget::changeEvent( QEvent* event )
+{
+  if ( event->type() == QEvent::EnabledChange )
+  {
+    updateLineEditStyle();
+  }
+}
+
+void QgsFieldExpressionWidget::currentFieldChanged( int i /* =0 */ )
 {
   Q_UNUSED( i );
-  bool isExpression;
-  QString fieldName = currentField( &isExpression );
-  bool isValid = true;
 
-  QFont font = mCombo->lineEdit()->font();
-  font.setItalic( isExpression );
-  mCombo->lineEdit()->setFont( font );
-
-  QPalette palette;
-  palette.setColor( QPalette::Text, Qt::black );
-  if ( isExpression )
-  {
-    QModelIndex idx = mFieldModel->indexFromName( fieldName );
-    if ( idx.isValid() )
-    {
-      isValid = mFieldModel->data( idx, QgsFieldModel::ExpressionValidityRole ).toBool();
-      if ( !isValid )
-      {
-        palette.setColor( QPalette::Text, Qt::red );
-      }
-    }
-  }
-  mCombo->lineEdit()->setPalette( palette );
+  updateLineEditStyle();
 
+  bool isExpression, isValid;
+  QString fieldName = currentField( &isExpression, &isValid );
   emit fieldChanged( fieldName );
   emit fieldChanged( fieldName, isValid );
 }
+
+void QgsFieldExpressionWidget::updateLineEditStyle()
+{
+  QPalette palette;
+  if ( !isEnabled() )
+  {
+    palette.setColor( QPalette::Text, Qt::gray );
+  }
+  else
+  {
+    bool isExpression, isValid;
+    currentField( &isExpression, &isValid );
+
+    QFont font = mCombo->lineEdit()->font();
+    font.setItalic( isExpression );
+    mCombo->lineEdit()->setFont( font );
+
+    if ( isExpression && !isValid )
+    {
+      palette.setColor( QPalette::Text, Qt::red );
+    }
+    else
+    {
+      palette.setColor( QPalette::Text, Qt::black );
+    }
+  }
+  mCombo->lineEdit()->setPalette( palette );
+}
diff --git a/src/gui/qgsfieldexpressionwidget.h b/src/gui/qgsfieldexpressionwidget.h
index c02de6d85ca..acf1cb33773 100644
--- a/src/gui/qgsfieldexpressionwidget.h
+++ b/src/gui/qgsfieldexpressionwidget.h
@@ -47,12 +47,15 @@ class GUI_EXPORT QgsFieldExpressionWidget : public QWidget
     /**
      * @brief currentField returns the currently selected field or expression if allowed
      * @param isExpression determines if the string returned is the name of a field or an expression
+     * @param isValid determines if the expression (or field) returned is valid
      */
-    QString currentField( bool *isExpression = 0 );
+    QString currentField( bool *isExpression = 0, bool *isValid = 0 );
 
     //! Returns the currently used layer
     QgsVectorLayer* layer();
 
+    void changeEvent( QEvent* event );
+
   signals:
     //! the signal is emitted when the currently selected field changes
     void fieldChanged( QString fieldName );
@@ -68,16 +71,18 @@ class GUI_EXPORT QgsFieldExpressionWidget : public QWidget
     void setLayer( QgsMapLayer* layer );
 
     //! sets the current field or expression in the widget
-    void setField( QString fieldName );
+    void setField( const QString fieldName );
 
   protected slots:
     //! open the expression dialog to edit the current or add a new expression
     void editExpression();
 
     //! when expression is edited by the user in the line edit
-    void expressionEdited( QString expression );
+    void expressionEdited( const QString expression );
 
-    void indexChanged( int i );
+    void currentFieldChanged( int i = 0 );
+
+    void updateLineEditStyle();
 
   private:
     QComboBox* mCombo;
diff --git a/src/gui/qgsfieldmodel.cpp b/src/gui/qgsfieldmodel.cpp
index 7ae026af67d..f8334298029 100644
--- a/src/gui/qgsfieldmodel.cpp
+++ b/src/gui/qgsfieldmodel.cpp
@@ -28,7 +28,7 @@ QgsFieldModel::QgsFieldModel( QObject *parent )
 {
 }
 
-QModelIndex QgsFieldModel::indexFromName( QString fieldName )
+QModelIndex QgsFieldModel::indexFromName( const QString fieldName )
 {
   int r = mFields.indexFromName( fieldName );
   QModelIndex idx = index( r, 0 );
@@ -104,7 +104,7 @@ void QgsFieldModel::setAllowExpression( bool allowExpression )
   }
 }
 
-QModelIndex QgsFieldModel::setExpression( QString expression )
+QModelIndex QgsFieldModel::setExpression( const QString expression )
 {
   if ( !mAllowExpression )
     return QModelIndex();
diff --git a/src/gui/qgsfieldmodel.h b/src/gui/qgsfieldmodel.h
index dda1d90ee64..7b3c8eb4ccc 100644
--- a/src/gui/qgsfieldmodel.h
+++ b/src/gui/qgsfieldmodel.h
@@ -49,7 +49,7 @@ class GUI_EXPORT QgsFieldModel : public QAbstractItemModel
     explicit QgsFieldModel( QObject *parent = 0 );
 
     //! return the index corresponding to a given fieldName
-    QModelIndex indexFromName( QString fieldName );
+    QModelIndex indexFromName( const QString fieldName );
 
     //! returns the currently used layer
     void setAllowExpression( bool allowExpression );
@@ -59,7 +59,7 @@ class GUI_EXPORT QgsFieldModel : public QAbstractItemModel
      * @brief setExpression sets a single expression to be added after the fields at the end of the model
      * @return the model index of the newly added expression
      */
-    QModelIndex setExpression( QString expression );
+    QModelIndex setExpression( const QString expression );
 
     //! remove expressions from the model
     void removeExpression();