diff --git a/src/analysis/processing/qgsalgorithmbuffer.cpp b/src/analysis/processing/qgsalgorithmbuffer.cpp
index 89b78826565d..9cb1bee15193 100644
--- a/src/analysis/processing/qgsalgorithmbuffer.cpp
+++ b/src/analysis/processing/qgsalgorithmbuffer.cpp
@@ -92,11 +92,6 @@ QVariantMap QgsBufferAlgorithm::processAlgorithm( const QVariantMap &parameters,
   if ( !source )
     throw QgsProcessingException( invalidSourceError( parameters, QStringLiteral( "INPUT" ) ) );
 
-  QString dest;
-  std::unique_ptr< QgsFeatureSink > sink( parameterAsSink( parameters, QStringLiteral( "OUTPUT" ), context, dest, source->fields(), Qgis::WkbType::MultiPolygon, source->sourceCrs() ) );
-  if ( !sink )
-    throw QgsProcessingException( invalidSinkError( parameters, QStringLiteral( "OUTPUT" ) ) );
-
   // fixed parameters
   const bool dissolve = parameterAsBoolean( parameters, QStringLiteral( "DISSOLVE" ), context );
   const bool keepDisjointSeparate = parameterAsBoolean( parameters, QStringLiteral( "SEPARATE_DISJOINT" ), context );
@@ -106,6 +101,12 @@ QVariantMap QgsBufferAlgorithm::processAlgorithm( const QVariantMap &parameters,
   const double miterLimit = parameterAsDouble( parameters, QStringLiteral( "MITER_LIMIT" ), context );
   const double bufferDistance = parameterAsDouble( parameters, QStringLiteral( "DISTANCE" ), context );
   const bool dynamicBuffer = QgsProcessingParameters::isDynamic( parameters, QStringLiteral( "DISTANCE" ) );
+
+  QString dest;
+  std::unique_ptr< QgsFeatureSink > sink( parameterAsSink( parameters, QStringLiteral( "OUTPUT" ), context, dest, source->fields(), Qgis::WkbType::MultiPolygon, source->sourceCrs(), keepDisjointSeparate ? QgsFeatureSink::RegeneratePrimaryKey : QgsFeatureSink::SinkFlags() ) );
+  if ( !sink )
+    throw QgsProcessingException( invalidSinkError( parameters, QStringLiteral( "OUTPUT" ) ) );
+
   QgsExpressionContext expressionContext = createExpressionContext( parameters, context, source.get() );
   QgsProperty bufferProperty;
   if ( dynamicBuffer )