diff --git a/src/analysis/vector/qgsoverlayanalyzer.cpp b/src/analysis/vector/qgsoverlayanalyzer.cpp
index d1d7aa81b046..f0bf0ffc528e 100644
--- a/src/analysis/vector/qgsoverlayanalyzer.cpp
+++ b/src/analysis/vector/qgsoverlayanalyzer.cpp
@@ -192,7 +192,7 @@ void QgsOverlayAnalyzer::combineFieldLists( QgsFields& fieldListA, const QgsFiel
 
   for ( int idx = 0; idx < fieldListB.count(); ++idx )
   {
-    QgsField field = fieldListB[idx];
+    QgsField field = fieldListB.at( idx );
     int count = 0;
     while ( names.contains( field.name() ) )
     {
diff --git a/src/app/qgsdelattrdialog.cpp b/src/app/qgsdelattrdialog.cpp
index bd69981c74ab..82b021539b3c 100644
--- a/src/app/qgsdelattrdialog.cpp
+++ b/src/app/qgsdelattrdialog.cpp
@@ -34,7 +34,7 @@ QgsDelAttrDialog::QgsDelAttrDialog( const QgsVectorLayer* vl )
     const QgsFields& layerAttributes = vl->fields();
     for ( int idx = 0; idx < layerAttributes.count(); ++idx )
     {
-      QListWidgetItem* item = new QListWidgetItem( layerAttributes[idx].name(), listBox2 );
+      QListWidgetItem* item = new QListWidgetItem( layerAttributes.at( idx ).name(), listBox2 );
       switch ( vl->fields().fieldOrigin( idx ) )
       {
         case QgsFields::OriginExpression:
diff --git a/src/app/qgsdiagramproperties.cpp b/src/app/qgsdiagramproperties.cpp
index 08b90111c49b..a090844c449f 100644
--- a/src/app/qgsdiagramproperties.cpp
+++ b/src/app/qgsdiagramproperties.cpp
@@ -184,14 +184,14 @@ QgsDiagramProperties::QgsDiagramProperties( QgsVectorLayer* layer,
   for ( int idx = 0; idx < layerFields.count(); ++idx )
   {
     QTreeWidgetItem *newItem = new QTreeWidgetItem( mAttributesTreeWidget );
-    QString name = QString( "\"%1\"" ).arg( layerFields[idx].name() );
+    QString name = QString( "\"%1\"" ).arg( layerFields.at( idx ).name() );
     newItem->setText( 0, name );
     newItem->setData( 0, Qt::UserRole, name );
     newItem->setFlags( newItem->flags() & ~Qt::ItemIsDropEnabled );
 
-    mDataDefinedXComboBox->addItem( layerFields[idx].name(), idx );
-    mDataDefinedYComboBox->addItem( layerFields[idx].name(), idx );
-    mDataDefinedVisibilityComboBox->addItem( layerFields[idx].name(), idx );
+    mDataDefinedXComboBox->addItem( layerFields.at( idx ).name(), idx );
+    mDataDefinedYComboBox->addItem( layerFields.at( idx ).name(), idx );
+    mDataDefinedVisibilityComboBox->addItem( layerFields.at( idx ).name(), idx );
   }
 
   const QgsDiagramRendererV2* dr = layer->diagramRenderer();
diff --git a/src/app/qgsfieldcalculator.cpp b/src/app/qgsfieldcalculator.cpp
index e0dd0980455e..43058e5f79ea 100644
--- a/src/app/qgsfieldcalculator.cpp
+++ b/src/app/qgsfieldcalculator.cpp
@@ -234,7 +234,7 @@ void QgsFieldCalculator::accept()
 
       for ( int idx = 0; idx < fields.count(); ++idx )
       {
-        if ( fields[idx].name() == mOutputFieldNameLineEdit->text() )
+        if ( fields.at( idx ).name() == mOutputFieldNameLineEdit->text() )
         {
           mAttributeId = idx;
           break;
diff --git a/src/app/qgsfieldsproperties.cpp b/src/app/qgsfieldsproperties.cpp
index cf8e843819d8..db9d70bf92b5 100644
--- a/src/app/qgsfieldsproperties.cpp
+++ b/src/app/qgsfieldsproperties.cpp
@@ -576,7 +576,7 @@ void QgsFieldsProperties::attributeAdded( int idx )
   const QgsFields &fields = mLayer->fields();
   int row = mFieldsList->rowCount();
   mFieldsList->insertRow( row );
-  setRow( row, idx, fields[idx] );
+  setRow( row, idx, fields.at( idx ) );
   mFieldsList->setCurrentCell( row, idx );
 
   for ( int i = idx + 1; i < mIndexedWidgets.count(); i++ )
diff --git a/src/app/qgsidentifyresultsdialog.cpp b/src/app/qgsidentifyresultsdialog.cpp
index 6cfdbef5d96a..906ed9f2fc03 100644
--- a/src/app/qgsidentifyresultsdialog.cpp
+++ b/src/app/qgsidentifyresultsdialog.cpp
@@ -493,7 +493,7 @@ void QgsIdentifyResultsDialog::addFeature( QgsVectorLayer *vlayer, const QgsFeat
     featItem->addChild( attrItem );
 
     attrItem->setData( 0, Qt::DisplayRole, vlayer->attributeDisplayName( i ) );
-    attrItem->setData( 0, Qt::UserRole, fields[i].name() );
+    attrItem->setData( 0, Qt::UserRole, fields.at( i ).name() );
     attrItem->setData( 0, Qt::UserRole + 1, i );
 
     attrItem->setData( 1, Qt::UserRole, value );
@@ -515,7 +515,7 @@ void QgsIdentifyResultsDialog::addFeature( QgsVectorLayer *vlayer, const QgsFeat
       attrItem->treeWidget()->setItemWidget( attrItem, 1, nullptr );
     }
 
-    if ( fields[i].name() == vlayer->displayField() )
+    if ( fields.at( i ).name() == vlayer->displayField() )
     {
       featItem->setText( 0, attrItem->text( 0 ) );
       featItem->setText( 1, attrItem->text( 1 ) );
@@ -560,11 +560,11 @@ void QgsIdentifyResultsDialog::addFeature( QgsVectorLayer *vlayer, const QgsFeat
     tblResults->setItem( j, 1, item );
 
     item = new QTableWidgetItem( QString::number( i ) );
-    if ( fields[i].name() == vlayer->displayField() )
+    if ( fields.at( i ).name() == vlayer->displayField() )
       item->setData( Qt::DisplayRole, vlayer->attributeDisplayName( i ) + " *" );
     else
       item->setData( Qt::DisplayRole, vlayer->attributeDisplayName( i ) );
-    item->setData( Qt::UserRole, fields[i].name() );
+    item->setData( Qt::UserRole, fields.at( i ).name() );
     item->setData( Qt::UserRole + 1, i );
     tblResults->setItem( j, 2, item );
 
@@ -765,7 +765,7 @@ void QgsIdentifyResultsDialog::addFeature( QgsRasterLayer *layer,
 
       QTreeWidgetItem *attrItem = new QTreeWidgetItem( QStringList() << QString::number( i ) << attrs.at( i ).toString() );
 
-      attrItem->setData( 0, Qt::DisplayRole, fields[i].name() );
+      attrItem->setData( 0, Qt::DisplayRole, fields.at( i ).name() );
 
       QVariant value = attrs.at( i );
       attrItem->setData( 1, Qt::DisplayRole, value );
@@ -1188,7 +1188,7 @@ void QgsIdentifyResultsDialog::doAction( QTreeWidgetItem *item, int action )
     const QgsFields& fields = layer->fields();
     for ( int fldIdx = 0; fldIdx < fields.count(); ++fldIdx )
     {
-      if ( fields[fldIdx].name() == fieldName )
+      if ( fields.at( fldIdx ).name() == fieldName )
       {
         idx = fldIdx;
         break;
@@ -1741,7 +1741,7 @@ void QgsIdentifyResultsDialog::copyFeatureAttributes()
       if ( attrIdx < 0 || attrIdx >= fields.count() )
         continue;
 
-      text += QString( "%1: %2\n" ).arg( fields[attrIdx].name(), it.value().toString() );
+      text += QString( "%1: %2\n" ).arg( fields.at( attrIdx ).name(), it.value().toString() );
     }
   }
   else if ( rlayer )
diff --git a/src/app/qgslabelpropertydialog.cpp b/src/app/qgslabelpropertydialog.cpp
index 99bd858de980..a57ca2be05b0 100644
--- a/src/app/qgslabelpropertydialog.cpp
+++ b/src/app/qgslabelpropertydialog.cpp
@@ -103,7 +103,7 @@ void QgsLabelPropertyDialog::init( const QString& layerId, const QString& provid
       {
         mLabelTextLineEdit->setText( attributeValues.at( mCurLabelField ).toString() );
         const QgsFields& layerFields = vlayer->fields();
-        switch ( layerFields[mCurLabelField].type() )
+        switch ( layerFields.at( mCurLabelField ).type() )
         {
           case QVariant::Double:
             mLabelTextLineEdit->setValidator( new QDoubleValidator( this ) );
diff --git a/src/app/qgsmergeattributesdialog.cpp b/src/app/qgsmergeattributesdialog.cpp
index 2e4ef7dbcdae..84e4a20b861c 100644
--- a/src/app/qgsmergeattributesdialog.cpp
+++ b/src/app/qgsmergeattributesdialog.cpp
@@ -358,7 +358,7 @@ QVariant QgsMergeAttributesDialog::calcStatistic( int col, QgsStatisticalSummary
 
   if ( values.isEmpty() )
   {
-    return QVariant( mVectorLayer->fields()[col].type() );
+    return QVariant( mVectorLayer->fields().at( col ).type() );
   }
 
   summary.calculate( values );
diff --git a/src/core/composer/qgscomposerattributetable.cpp b/src/core/composer/qgscomposerattributetable.cpp
index 17042e982881..b27b8d56f115 100644
--- a/src/core/composer/qgscomposerattributetable.cpp
+++ b/src/core/composer/qgscomposerattributetable.cpp
@@ -241,7 +241,7 @@ void QgsComposerAttributeTable::setDisplayAttributes( const QSet<int>& attr, boo
       }
       QString currentAlias = mVectorLayer->attributeDisplayName( attrIdx );
       QgsComposerTableColumn* col = new QgsComposerTableColumn;
-      col->setAttribute( fields[attrIdx].name() );
+      col->setAttribute( fields.at( attrIdx ).name() );
       col->setHeading( currentAlias );
       mColumns.append( col );
     }
@@ -652,7 +652,7 @@ bool QgsComposerAttributeTable::readXml( const QDomElement& itemElem, const QDom
       //find corresponding column
       Q_FOREACH ( QgsComposerTableColumn* column, mColumns )
       {
-        if ( column->attribute() == fields[attribute].name() )
+        if ( column->attribute() == fields.at( attribute ).name() )
         {
           column->setSortByRank( i + 1 );
           column->setSortOrder( order );
diff --git a/src/core/composer/qgscomposerattributetablev2.cpp b/src/core/composer/qgscomposerattributetablev2.cpp
index a52f05a7586d..8c2c2c3627e8 100644
--- a/src/core/composer/qgscomposerattributetablev2.cpp
+++ b/src/core/composer/qgscomposerattributetablev2.cpp
@@ -338,7 +338,7 @@ void QgsComposerAttributeTableV2::setDisplayAttributes( const QSet<int>& attr, b
       }
       QString currentAlias = source->attributeDisplayName( attrIdx );
       QgsComposerTableColumn* col = new QgsComposerTableColumn;
-      col->setAttribute( fields[attrIdx].name() );
+      col->setAttribute( fields.at( attrIdx ).name() );
       col->setHeading( currentAlias );
       mColumns.append( col );
     }
diff --git a/src/core/qgsactionmanager.cpp b/src/core/qgsactionmanager.cpp
index 177693fc0ecc..b8764e43c333 100644
--- a/src/core/qgsactionmanager.cpp
+++ b/src/core/qgsactionmanager.cpp
@@ -210,13 +210,13 @@ QString QgsActionManager::expandAction( QString action, const QgsAttributeMap &a
       switch ( i )
       {
         case 0:
-          to_replace = "[%" + fields[attrIdx].name() + ']';
+          to_replace = "[%" + fields.at( attrIdx ).name() + ']';
           break;
         case 1:
           to_replace = "[%" + mLayer->attributeDisplayName( attrIdx ) + ']';
           break;
         case 2:
-          to_replace = '%' + fields[attrIdx].name();
+          to_replace = '%' + fields.at( attrIdx ).name();
           break;
         case 3:
           to_replace = '%' + mLayer->attributeDisplayName( attrIdx );
diff --git a/src/core/qgsgml.cpp b/src/core/qgsgml.cpp
index f7a2f3e07911..d159d11df0bd 100644
--- a/src/core/qgsgml.cpp
+++ b/src/core/qgsgml.cpp
@@ -294,7 +294,7 @@ QgsGmlStreamingParser::QgsGmlStreamingParser( const QString& typeName,
   mThematicAttributes.clear();
   for ( int i = 0; i < fields.size(); i++ )
   {
-    mThematicAttributes.insert( fields[i].name(), qMakePair( i, fields[i] ) );
+    mThematicAttributes.insert( fields.at( i ).name(), qMakePair( i, fields.at( i ) ) );
   }
 
   mEndian = QgsApplication::endian();
@@ -355,13 +355,13 @@ QgsGmlStreamingParser::QgsGmlStreamingParser( const QList<LayerProperties>& laye
   mThematicAttributes.clear();
   for ( int i = 0; i < fields.size(); i++ )
   {
-    QMap< QString, QPair<QString, QString> >::const_iterator att_it = mapFieldNameToSrcLayerNameFieldName.constFind( fields[i].name() );
+    QMap< QString, QPair<QString, QString> >::const_iterator att_it = mapFieldNameToSrcLayerNameFieldName.constFind( fields.at( i ).name() );
     if ( att_it != mapFieldNameToSrcLayerNameFieldName.constEnd() )
     {
       if ( mLayerProperties.size() == 1 )
-        mThematicAttributes.insert( att_it.value().second, qMakePair( i, fields[i] ) );
+        mThematicAttributes.insert( att_it.value().second, qMakePair( i, fields.at( i ) ) );
       else
-        mThematicAttributes.insert( stripNS( att_it.value().first ) + "|" + att_it.value().second, qMakePair( i, fields[i] ) );
+        mThematicAttributes.insert( stripNS( att_it.value().first ) + "|" + att_it.value().second, qMakePair( i, fields.at( i ) ) );
     }
   }
   bool alreadyFoundGeometry = false;
diff --git a/src/core/qgsvectorfilewriter.cpp b/src/core/qgsvectorfilewriter.cpp
index 2766d1136a4f..7aeaf97bf5d4 100644
--- a/src/core/qgsvectorfilewriter.cpp
+++ b/src/core/qgsvectorfilewriter.cpp
@@ -398,13 +398,13 @@ void QgsVectorFileWriter::init( QString vectorFileName,
 
   for ( int fldIdx = 0; fldIdx < fields.count(); ++fldIdx )
   {
-    QgsField attrField = fields[fldIdx];
+    QgsField attrField = fields.at( fldIdx );
 
     OGRFieldType ogrType = OFTString; //default to string
 
     if ( fieldValueConverter )
     {
-      attrField = fieldValueConverter->fieldDefinition( fields[fldIdx] );
+      attrField = fieldValueConverter->fieldDefinition( fields.at( fldIdx ) );
     }
 
     int ogrWidth = attrField.length();
@@ -489,7 +489,7 @@ void QgsVectorFileWriter::init( QString vectorFileName,
         name = QString( "ogc_fid%1" ).arg( i );
 
         int j;
-        for ( j = 0; j < fields.size() && name.compare( fields[j].name(), Qt::CaseInsensitive ) != 0; j++ )
+        for ( j = 0; j < fields.size() && name.compare( fields.at( j ).name(), Qt::CaseInsensitive ) != 0; j++ )
           ;
 
         if ( j == fields.size() )
diff --git a/src/gui/qgsquerybuilder.cpp b/src/gui/qgsquerybuilder.cpp
index ea7cd846b409..b211face3510 100644
--- a/src/gui/qgsquerybuilder.cpp
+++ b/src/gui/qgsquerybuilder.cpp
@@ -77,7 +77,7 @@ void QgsQueryBuilder::populateFields()
       // only consider native fields
       continue;
     }
-    QStandardItem *myItem = new QStandardItem( fields[idx].name() );
+    QStandardItem *myItem = new QStandardItem( fields.at( idx ).name() );
     myItem->setData( idx );
     myItem->setEditable( false );
     mModelFields->insertRow( mModelFields->rowCount(), myItem );
diff --git a/src/gui/qgssearchquerybuilder.cpp b/src/gui/qgssearchquerybuilder.cpp
index 998aa959f342..be13a86cdb66 100644
--- a/src/gui/qgssearchquerybuilder.cpp
+++ b/src/gui/qgssearchquerybuilder.cpp
@@ -77,7 +77,7 @@ void QgsSearchQueryBuilder::populateFields()
   const QgsFields& fields = mLayer->fields();
   for ( int idx = 0; idx < fields.count(); ++idx )
   {
-    QString fieldName = fields[idx].name();
+    QString fieldName = fields.at( idx ).name();
     mFieldMap[fieldName] = idx;
     QStandardItem *myItem = new QStandardItem( fieldName );
     myItem->setEditable( false );
diff --git a/src/providers/db2/qgsdb2provider.cpp b/src/providers/db2/qgsdb2provider.cpp
index e551ce07c4b6..cc370e166410 100644
--- a/src/providers/db2/qgsdb2provider.cpp
+++ b/src/providers/db2/qgsdb2provider.cpp
@@ -1332,7 +1332,7 @@ QgsVectorLayerImport::ImportError QgsDb2Provider::createEmptyLayer( const QStrin
     QString pk = primaryKey = "QGS_FID";
     for ( int i = 0; i < fieldCount; ++i )
     {
-      if ( fields[i].name() == primaryKey )
+      if ( fields.at( i ).name() == primaryKey )
       {
         // it already exists, try again with a new name
         primaryKey = QString( "%1_%2" ).arg( pk ).arg( index++ );
@@ -1345,10 +1345,10 @@ QgsVectorLayerImport::ImportError QgsDb2Provider::createEmptyLayer( const QStrin
     // search for the passed field
     for ( int i = 0; i < fieldCount; ++i )
     {
-      if ( fields[i].name() == primaryKey )
+      if ( fields.at( i ).name() == primaryKey )
       {
         // found, get the field type
-        QgsField fld = fields[i];
+        QgsField fld = fields.at( i );
         if ( convertField( fld ) )
         {
           primaryKeyType = fld.typeName();
diff --git a/src/providers/memory/qgsmemoryprovider.cpp b/src/providers/memory/qgsmemoryprovider.cpp
index 8047c6618356..d68166069712 100644
--- a/src/providers/memory/qgsmemoryprovider.cpp
+++ b/src/providers/memory/qgsmemoryprovider.cpp
@@ -262,7 +262,7 @@ QString QgsMemoryProvider::dataSourceUri( bool expandAuthConfig ) const
   QgsAttributeList attrs = const_cast<QgsMemoryProvider *>( this )->attributeIndexes();
   for ( int i = 0; i < attrs.size(); i++ )
   {
-    QgsField field = mFields[attrs[i]];
+    QgsField field = mFields.at( attrs[i] );
     QString fieldDef = field.name();
     fieldDef.append( QString( ":%2(%3,%4)" ).arg( field.typeName() ).arg( field.length() ).arg( field.precision() ) );
     uri.addQueryItem( "field", fieldDef );
diff --git a/src/providers/mssql/qgsmssqlprovider.cpp b/src/providers/mssql/qgsmssqlprovider.cpp
index 450785e505fc..3b28d0ff8b20 100644
--- a/src/providers/mssql/qgsmssqlprovider.cpp
+++ b/src/providers/mssql/qgsmssqlprovider.cpp
@@ -1669,7 +1669,7 @@ QgsVectorLayerImport::ImportError QgsMssqlProvider::createEmptyLayer( const QStr
     QString pk = primaryKey = "qgs_fid";
     for ( int i = 0, n = fields.size(); i < n; ++i )
     {
-      if ( fields[i].name() == primaryKey )
+      if ( fields.at( i ).name() == primaryKey )
       {
         // it already exists, try again with a new name
         primaryKey = QString( "%1_%2" ).arg( pk ).arg( index++ );
@@ -1682,10 +1682,10 @@ QgsVectorLayerImport::ImportError QgsMssqlProvider::createEmptyLayer( const QStr
     // search for the passed field
     for ( int i = 0, n = fields.size(); i < n; ++i )
     {
-      if ( fields[i].name() == primaryKey )
+      if ( fields.at( i ).name() == primaryKey )
       {
         // found, get the field type
-        QgsField fld = fields[i];
+        QgsField fld = fields.at( i );
         if ( convertField( fld ) )
         {
           primaryKeyType = fld.typeName();
@@ -1830,7 +1830,7 @@ QgsVectorLayerImport::ImportError QgsMssqlProvider::createEmptyLayer( const QStr
     QList<QgsField> flist;
     for ( int i = 0, n = fields.size(); i < n; ++i )
     {
-      QgsField fld = fields[i];
+      QgsField fld = fields.at( i );
       if ( oldToNewAttrIdxMap && fld.name() == primaryKey )
       {
         oldToNewAttrIdxMap->insert( fields.fieldNameIndex( fld.name() ), 0 );
diff --git a/src/providers/oracle/qgsoraclefeatureiterator.cpp b/src/providers/oracle/qgsoraclefeatureiterator.cpp
index ee9eab0607fb..a8db8272055f 100644
--- a/src/providers/oracle/qgsoraclefeatureiterator.cpp
+++ b/src/providers/oracle/qgsoraclefeatureiterator.cpp
@@ -452,14 +452,14 @@ bool QgsOracleFeatureIterator::openQuery( QString whereClause, bool showLog )
         break;
 
       case pktInt:
-        query += delim + QgsOracleProvider::quotedIdentifier( mSource->mFields[ mSource->mPrimaryKeyAttrs[0] ].name() );
+        query += delim + QgsOracleProvider::quotedIdentifier( mSource->mFields.at( mSource->mPrimaryKeyAttrs[0] ).name() );
         delim = ",";
         break;
 
       case pktFidMap:
         Q_FOREACH ( int idx, mSource->mPrimaryKeyAttrs )
         {
-          query += delim + mConnection->fieldExpression( mSource->mFields[idx] );
+          query += delim + mConnection->fieldExpression( mSource->mFields.at( idx ) );
           delim = ",";
         }
         break;
@@ -475,7 +475,7 @@ bool QgsOracleFeatureIterator::openQuery( QString whereClause, bool showLog )
       if ( mSource->mPrimaryKeyAttrs.contains( idx ) )
         continue;
 
-      query += delim + mConnection->fieldExpression( mSource->mFields[idx] );
+      query += delim + mConnection->fieldExpression( mSource->mFields.at( idx ) );
     }
 
     query += QString( " FROM %1 \"FEATUREREQUEST\"" ).arg( mSource->mQuery );
diff --git a/src/providers/oracle/qgsoracleprovider.cpp b/src/providers/oracle/qgsoracleprovider.cpp
index bd92d3438163..6fb54f00e61b 100644
--- a/src/providers/oracle/qgsoracleprovider.cpp
+++ b/src/providers/oracle/qgsoracleprovider.cpp
@@ -181,7 +181,7 @@ QgsOracleProvider::QgsOracleProvider( QString const & uri )
       Q_FOREACH ( int idx, mPrimaryKeyAttrs )
       {
         Q_ASSERT( idx >= 0 && idx < mAttributeFields.size() );
-        key += delim + mAttributeFields[ idx ].name();
+        key += delim + mAttributeFields.at( idx ).name();
         delim = ",";
       }
     }
@@ -416,7 +416,7 @@ QString QgsOracleUtils::whereClause( QgsFeatureId featureId, const QgsFields& fi
   {
     case pktInt:
       Q_ASSERT( primaryKeyAttrs.size() == 1 );
-      whereClause = QString( "%1=%2" ).arg( QgsOracleConn::quotedIdentifier( fields[ primaryKeyAttrs[0] ].name() ) ).arg( featureId );
+      whereClause = QString( "%1=%2" ).arg( QgsOracleConn::quotedIdentifier( fields.at( primaryKeyAttrs[0] ).name() ) ).arg( featureId );
       break;
 
     case pktRowId:
@@ -966,9 +966,9 @@ bool QgsOracleProvider::determinePrimaryKey()
     int idx = fieldNameIndex( mUri.keyColumn() );
 
     if ( idx >= 0 && (
-           mAttributeFields[idx].type() == QVariant::Int ||
-           mAttributeFields[idx].type() == QVariant::LongLong ||
-           mAttributeFields[idx].type() == QVariant::Double
+           mAttributeFields.at( idx ).type() == QVariant::Int ||
+           mAttributeFields.at( idx ).type() == QVariant::LongLong ||
+           mAttributeFields.at( idx ).type() == QVariant::Double
          ) )
     {
       if ( mUseEstimatedMetadata || uniqueData( mQuery, primaryKey ) )
@@ -1299,7 +1299,7 @@ bool QgsOracleProvider::addFeatures( QgsFeatureList &flist )
         }
         else
         {
-          values += delim + quotedValue( v, mAttributeFields[idx].type() );
+          values += delim + quotedValue( v, mAttributeFields.at( idx ).type() );
         }
       }
       else
@@ -2091,7 +2091,7 @@ bool QgsOracleProvider::setSubsetString( const QString& theSQL, bool updateFeatu
   }
   qry.finish();
 
-  if ( mPrimaryKeyType == pktInt && !uniqueData( mQuery, mAttributeFields[ mPrimaryKeyAttrs[0] ].name() ) )
+  if ( mPrimaryKeyType == pktInt && !uniqueData( mQuery, mAttributeFields.at( mPrimaryKeyAttrs[0] ).name() ) )
   {
     mSqlWhereClause = prevWhere;
     return false;
@@ -2649,7 +2649,7 @@ QgsVectorLayerImport::ImportError QgsOracleProvider::createEmptyLayer(
     int idx = fields.indexFromName( primaryKey );
     if ( idx >= 0 )
     {
-      QgsField fld = fields[idx];
+      QgsField fld = fields.at( idx );
       if ( convertField( fld ) )
       {
         primaryKeyType = fld.typeName();
@@ -2856,7 +2856,7 @@ QgsVectorLayerImport::ImportError QgsOracleProvider::createEmptyLayer(
     QList<QgsField> launderedFields;
     for ( int i = 0; i < fields.size(); i++ )
     {
-      QgsField fld = fields[i];
+      QgsField fld = fields.at( i );
 
       QString name = fld.name().left( 30 ).toUpper();
 
diff --git a/src/providers/postgres/qgspostgresprovider.cpp b/src/providers/postgres/qgspostgresprovider.cpp
index 3b4b43bfd557..4e79cc67cfff 100644
--- a/src/providers/postgres/qgspostgresprovider.cpp
+++ b/src/providers/postgres/qgspostgresprovider.cpp
@@ -544,12 +544,12 @@ QString QgsPostgresUtils::whereClause( QgsFeatureId featureId, const QgsFields&
 
     case pktInt:
       Q_ASSERT( pkAttrs.size() == 1 );
-      whereClause = QString( "%1=%2" ).arg( QgsPostgresConn::quotedIdentifier( fields[ pkAttrs[0] ].name() ) ).arg( FID2PKINT( featureId ) );
+      whereClause = QString( "%1=%2" ).arg( QgsPostgresConn::quotedIdentifier( fields.at( pkAttrs[0] ).name() ) ).arg( FID2PKINT( featureId ) );
       break;
 
     case pktUint64:
       Q_ASSERT( pkAttrs.size() == 1 );
-      whereClause = QString( "%1=%2" ).arg( QgsPostgresConn::quotedIdentifier( fields[ pkAttrs[0] ].name() ) ).arg( featureId );
+      whereClause = QString( "%1=%2" ).arg( QgsPostgresConn::quotedIdentifier( fields.at( pkAttrs[0] ).name() ) ).arg( featureId );
       break;
 
     case pktFidMap:
@@ -565,7 +565,7 @@ QString QgsPostgresUtils::whereClause( QgsFeatureId featureId, const QgsFields&
         for ( int i = 0; i < pkAttrs.size(); i++ )
         {
           int idx = pkAttrs[i];
-          QgsField fld = fields[ idx ];
+          QgsField fld = fields.at( idx );
 
           whereClause += delim + conn->fieldExpression( fld );
           if ( pkVals[i].isNull() )
@@ -607,7 +607,7 @@ QString QgsPostgresUtils::whereClause( const QgsFeatureIds& featureIds, const Qg
       if ( !featureIds.isEmpty() )
       {
         QString delim;
-        expr = QString( "%1 IN (" ).arg(( pkType == pktOid ? "oid" : QgsPostgresConn::quotedIdentifier( fields[ pkAttrs[0] ].name() ) ) );
+        expr = QString( "%1 IN (" ).arg(( pkType == pktOid ? "oid" : QgsPostgresConn::quotedIdentifier( fields.at( pkAttrs[0] ).name() ) ) );
 
         Q_FOREACH ( const QgsFeatureId featureId, featureIds )
         {
@@ -3489,7 +3489,7 @@ QgsVectorLayerImport::ImportError QgsPostgresProvider::createEmptyLayer( const Q
     QString pk = primaryKey = "id";
     for ( int fldIdx = 0; fldIdx < fields.count(); ++fldIdx )
     {
-      if ( fields[fldIdx].name() == primaryKey )
+      if ( fields.at( fldIdx ).name() == primaryKey )
       {
         // it already exists, try again with a new name
         primaryKey = QString( "%1_%2" ).arg( pk ).arg( index++ );
@@ -3502,10 +3502,10 @@ QgsVectorLayerImport::ImportError QgsPostgresProvider::createEmptyLayer( const Q
     // search for the passed field
     for ( int fldIdx = 0; fldIdx < fields.count(); ++fldIdx )
     {
-      if ( fields[fldIdx].name() == primaryKey )
+      if ( fields.at( fldIdx ).name() == primaryKey )
       {
         // found, get the field type
-        QgsField fld = fields[fldIdx];
+        QgsField fld = fields.at( fldIdx );
         if ( convertField( fld, options ) )
         {
           primaryKeyType = fld.typeName();
@@ -3658,7 +3658,7 @@ QgsVectorLayerImport::ImportError QgsPostgresProvider::createEmptyLayer( const Q
     QList<QgsField> flist;
     for ( int fldIdx = 0; fldIdx < fields.count(); ++fldIdx )
     {
-      QgsField fld = fields[fldIdx];
+      QgsField fld = fields.at( fldIdx );
 
       if ( fld.name() == geometryColumn )
       {
diff --git a/src/providers/spatialite/qgsspatialiteprovider.cpp b/src/providers/spatialite/qgsspatialiteprovider.cpp
index dd8e74a563a7..0582c95b62c4 100644
--- a/src/providers/spatialite/qgsspatialiteprovider.cpp
+++ b/src/providers/spatialite/qgsspatialiteprovider.cpp
@@ -144,7 +144,7 @@ QgsSpatiaLiteProvider::createEmptyLayer( const QString& uri,
       QString pk = primaryKey = "pk";
       for ( int fldIdx = 0; fldIdx < fields.count(); ++fldIdx )
       {
-        if ( fields[fldIdx].name() == primaryKey )
+        if ( fields.at( fldIdx ).name() == primaryKey )
         {
           // it already exists, try again with a new name
           primaryKey = QString( "%1_%2" ).arg( pk ).arg( index++ );
@@ -157,10 +157,10 @@ QgsSpatiaLiteProvider::createEmptyLayer( const QString& uri,
       // search for the passed field
       for ( int fldIdx = 0; fldIdx < fields.count(); ++fldIdx )
       {
-        if ( fields[fldIdx].name() == primaryKey )
+        if ( fields.at( fldIdx ).name() == primaryKey )
         {
           // found, get the field type
-          QgsField fld = fields[fldIdx];
+          QgsField fld = fields.at( fldIdx );
           if ( convertField( fld ) )
           {
             primaryKeyType = fld.typeName();
@@ -357,7 +357,7 @@ QgsSpatiaLiteProvider::createEmptyLayer( const QString& uri,
     QList<QgsField> flist;
     for ( int fldIdx = 0; fldIdx < fields.count(); ++fldIdx )
     {
-      QgsField fld = fields[fldIdx];
+      QgsField fld = fields.at( fldIdx );
       if ( fld.name() == primaryKey )
         continue;
 
diff --git a/src/providers/wfs/qgswfsprovider.cpp b/src/providers/wfs/qgswfsprovider.cpp
index d1f4b9c13a1f..d8f6ead1f6a0 100644
--- a/src/providers/wfs/qgswfsprovider.cpp
+++ b/src/providers/wfs/qgswfsprovider.cpp
@@ -618,9 +618,9 @@ bool QgsWFSProvider::processSQL( const QString& sqlString, QString& errorMsg, QS
         return false;
       }
 
-      QgsField field( fieldName, tableFields[idx].type(), tableFields[idx].typeName() );
+      QgsField field( fieldName, tableFields.at( idx ).type(), tableFields.at( idx ).typeName() );
       mapFieldNameToSrcLayerNameFieldName[ field.name()] =
-        QPair<QString, QString>( columnTableTypename, tableFields[idx].name() );
+        QPair<QString, QString>( columnTableTypename, tableFields.at( idx ).name() );
       mShared->mFields.append( field );
     }
   }
diff --git a/src/server/qgswfsprojectparser.cpp b/src/server/qgswfsprojectparser.cpp
index 0cd60decbfe0..f9d42afa9a7a 100644
--- a/src/server/qgswfsprojectparser.cpp
+++ b/src/server/qgswfsprojectparser.cpp
@@ -465,7 +465,7 @@ void QgsWfsProjectParser::describeFeatureType( const QString& aTypeName, QDomEle
           //xsd:element
           QDomElement attElem = doc.createElement( "element"/*xsd:element*/ );
           attElem.setAttribute( "name", attributeName );
-          QVariant::Type attributeType = fields[idx].type();
+          QVariant::Type attributeType = fields.at( idx ).type();
           if ( attributeType == QVariant::Int )
             attElem.setAttribute( "type", "integer" );
           else if ( attributeType == QVariant::LongLong )
diff --git a/src/server/qgswmsserver.cpp b/src/server/qgswmsserver.cpp
index d70dafb3c162..97e6630400cd 100644
--- a/src/server/qgswmsserver.cpp
+++ b/src/server/qgswmsserver.cpp
@@ -2305,13 +2305,13 @@ int QgsWmsServer::featureInfoFromVectorLayer( QgsVectorLayer* layer,
       for ( int i = 0; i < featureAttributes.count(); ++i )
       {
         //skip attribute if it is explicitly excluded from WMS publication
-        if ( excludedAttributes.contains( fields[i].name() ) )
+        if ( excludedAttributes.contains( fields.at( i ).name() ) )
         {
           continue;
         }
 #ifdef HAVE_SERVER_PYTHON_PLUGINS
         //skip attribute if it is excluded by access control
-        if ( !attributes.contains( fields[i].name() ) )
+        if ( !attributes.contains( fields.at( i ).name() ) )
         {
           continue;
         }