diff --git a/src/core/qgsdiagramrenderer.cpp b/src/core/qgsdiagramrenderer.cpp
index cd339e881e6..24a78f0501d 100644
--- a/src/core/qgsdiagramrenderer.cpp
+++ b/src/core/qgsdiagramrenderer.cpp
@@ -536,6 +536,11 @@ void QgsDiagramRenderer::_readXml( const QDomElement &elem, const QgsReadWriteCo
   {
     mDiagram.reset( new QgsHistogramDiagram() );
   }
+  else
+  {
+    // unknown diagram type -- default to histograms
+    mDiagram.reset( new QgsHistogramDiagram() );
+  }
   mShowAttributeLegend = ( elem.attribute( QStringLiteral( "attributeLegend" ), QStringLiteral( "1" ) ) != QLatin1String( "0" ) );
 }