diff --git a/python/gui/auto_generated/qgsnewvectorlayerdialog.sip.in b/python/gui/auto_generated/qgsnewvectorlayerdialog.sip.in
index d7f122c86620..fa5a81b394fa 100644
--- a/python/gui/auto_generated/qgsnewvectorlayerdialog.sip.in
+++ b/python/gui/auto_generated/qgsnewvectorlayerdialog.sip.in
@@ -107,6 +107,10 @@ Sets the ``crs`` value for the new layer in the dialog.
 .. versionadded:: 3.0
 %End
 
+  public slots:
+    virtual void accept();
+
+
 };
 
 /************************************************************************
diff --git a/src/gui/qgsnewvectorlayerdialog.cpp b/src/gui/qgsnewvectorlayerdialog.cpp
index bdd9d14a5386..f41650ef856d 100644
--- a/src/gui/qgsnewvectorlayerdialog.cpp
+++ b/src/gui/qgsnewvectorlayerdialog.cpp
@@ -28,6 +28,7 @@
 #include "qgsogrprovider.h"
 #include "qgsgui.h"
 #include "qgsiconutils.h"
+#include "qgsfileutils.h"
 
 #include <QPushButton>
 #include <QComboBox>
@@ -109,21 +110,9 @@ QgsNewVectorLayerDialog::QgsNewVectorLayerDialog( QWidget *parent, Qt::WindowFla
   mAttributeView->addTopLevelItem( new QTreeWidgetItem( QStringList() << QStringLiteral( "id" ) << QStringLiteral( "Integer" ) << QStringLiteral( "10" ) << QString() ) );
   connect( mNameEdit, &QLineEdit::textChanged, this, &QgsNewVectorLayerDialog::nameChanged );
   connect( mAttributeView, &QTreeWidget::itemSelectionChanged, this, &QgsNewVectorLayerDialog::selectionChanged );
-  connect( mGeometryTypeBox, static_cast<void( QComboBox::* )( int )>( &QComboBox::currentIndexChanged ), this, [ = ]( int index )
+  connect( mGeometryTypeBox, static_cast<void( QComboBox::* )( int )>( &QComboBox::currentIndexChanged ), this, [ = ]( int )
   {
-    QString fileName = mFileName->filePath();
-    if ( !fileName.isEmpty() )
-    {
-      if ( index == 0 )
-      {
-        fileName = fileName.replace( fileName.lastIndexOf( QLatin1String( ".shp" ), -1, Qt::CaseInsensitive ), 4, QLatin1String( ".dbf" ) );
-      }
-      else
-      {
-        fileName = fileName.replace( fileName.lastIndexOf( QLatin1String( ".dbf" ), -1, Qt::CaseInsensitive ), 4, QLatin1String( ".shp" ) );
-      }
-      mFileName->setFilePath( fileName );
-    }
+    updateExtension();
     checkOk();
   } );
 
@@ -293,6 +282,39 @@ QString QgsNewVectorLayerDialog::runAndCreateLayer( QWidget *parent, QString *pE
   return res;
 }
 
+void QgsNewVectorLayerDialog::updateExtension()
+{
+  QString fileName = filename();
+  const QString fileformat = selectedFileFormat();
+  const QgsWkbTypes::Type geometrytype = selectedType();
+  if ( fileformat == QLatin1String( "ESRI Shapefile" ) )
+  {
+    if ( geometrytype != QgsWkbTypes::NoGeometry )
+    {
+      fileName = fileName.replace( fileName.lastIndexOf( QLatin1String( ".dbf" ), -1, Qt::CaseInsensitive ), 4, QLatin1String( ".shp" ) );
+      fileName = QgsFileUtils::ensureFileNameHasExtension( fileName, { QStringLiteral( "shp" ) } );
+    }
+    else
+    {
+      fileName = fileName.replace( fileName.lastIndexOf( QLatin1String( ".shp" ), -1, Qt::CaseInsensitive ), 4, QLatin1String( ".dbf" ) );
+      fileName = QgsFileUtils::ensureFileNameHasExtension( fileName, { QStringLiteral( "dbf" ) } );
+    }
+  }
+  setFilename( fileName );
+
+}
+
+void QgsNewVectorLayerDialog::accept()
+{
+  updateExtension();
+
+  if ( QFile::exists( filename() ) && QMessageBox::warning( this, tr( "New ShapeFile Layer" ), tr( "The layer already exists. Are you sure you want to overwrite the existing file?" ),
+       QMessageBox::Yes | QMessageBox::Cancel, QMessageBox::Cancel ) != QMessageBox::Yes )
+    return;
+
+  QDialog::accept();
+}
+
 QString QgsNewVectorLayerDialog::execAndCreateLayer( QString &errorMessage, QWidget *parent, const QString &initialPath, QString *encoding, const QgsCoordinateReferenceSystem &crs )
 {
   errorMessage.clear();
@@ -305,12 +327,10 @@ QString QgsNewVectorLayerDialog::execAndCreateLayer( QString &errorMessage, QWid
     return QString();
   }
 
-  if ( QFile::exists( geomDialog.filename() ) && QMessageBox::warning( parent, tr( "New ShapeFile Layer" ), tr( "The layer already exists. Are you sure you want to overwrite the existing file?" ),
-       QMessageBox::Yes | QMessageBox::Cancel, QMessageBox::Cancel ) != QMessageBox::Yes )
-    return QString();
-
-  const QgsWkbTypes::Type geometrytype = geomDialog.selectedType();
   const QString fileformat = geomDialog.selectedFileFormat();
+  const QgsWkbTypes::Type geometrytype = geomDialog.selectedType();
+  QString fileName = geomDialog.filename();
+
   const QString enc = geomDialog.selectedFileEncoding();
   QgsDebugMsg( QStringLiteral( "New file format will be: %1" ).arg( fileformat ) );
 
@@ -318,17 +338,6 @@ QString QgsNewVectorLayerDialog::execAndCreateLayer( QString &errorMessage, QWid
   geomDialog.attributes( attributes );
 
   QgsSettings settings;
-  QString fileName = geomDialog.filename();
-  if ( fileformat == QLatin1String( "ESRI Shapefile" ) && ( geometrytype != QgsWkbTypes::NoGeometry && !fileName.endsWith( QLatin1String( ".shp" ), Qt::CaseInsensitive ) ) )
-    fileName += QLatin1String( ".shp" );
-  else if ( fileformat == QLatin1String( "ESRI Shapefile" ) && ( geometrytype == QgsWkbTypes::NoGeometry && !fileName.endsWith( QLatin1String( ".dbf" ), Qt::CaseInsensitive ) ) )
-  {
-    if ( fileName.endsWith( QLatin1String( ".shp" ), Qt::CaseInsensitive ) )
-      fileName = fileName.replace( fileName.lastIndexOf( QLatin1String( ".shp" ), -1, Qt::CaseInsensitive ), 4, QLatin1String( ".dbf" ) );
-    else
-      fileName += QLatin1String( ".dbf" );
-  }
-
   settings.setValue( QStringLiteral( "UI/lastVectorFileFilterDir" ), QFileInfo( fileName ).absolutePath() );
   settings.setValue( QStringLiteral( "UI/encoding" ), enc );
 
diff --git a/src/gui/qgsnewvectorlayerdialog.h b/src/gui/qgsnewvectorlayerdialog.h
index 2890d6bad9fa..c9d283166104 100644
--- a/src/gui/qgsnewvectorlayerdialog.h
+++ b/src/gui/qgsnewvectorlayerdialog.h
@@ -112,6 +112,9 @@ class GUI_EXPORT QgsNewVectorLayerDialog: public QDialog, private Ui::QgsNewVect
      */
     void setCrs( const QgsCoordinateReferenceSystem &crs );
 
+  public slots:
+    void accept() override;
+
   private slots:
     void mAddAttributeButton_clicked();
     void mRemoveAttributeButton_clicked();
@@ -126,6 +129,8 @@ class GUI_EXPORT QgsNewVectorLayerDialog: public QDialog, private Ui::QgsNewVect
 
   private:
     QPushButton *mOkButton = nullptr;
+
+    void updateExtension();
 };
 
 #endif //qgsnewvectorlayerdialog_H