diff --git a/Code/Mantid/MantidPlot/src/Mantid/InstrumentWidget/Shape2DCollection.cpp b/Code/Mantid/MantidPlot/src/Mantid/InstrumentWidget/Shape2DCollection.cpp
index 7c6eb09116c3a62b41c8a4dc6991e8c5121cc71a..debedc4f95254b377d0840669a9bb6d2681855a5 100644
--- a/Code/Mantid/MantidPlot/src/Mantid/InstrumentWidget/Shape2DCollection.cpp
+++ b/Code/Mantid/MantidPlot/src/Mantid/InstrumentWidget/Shape2DCollection.cpp
@@ -264,9 +264,9 @@ bool Shape2DCollection::selectAtXY(int x,int y)
 /**
  * Select a shape with index i.
  */
-void Shape2DCollection::select(size_t i)
+void Shape2DCollection::select(int i)
 {
-  if (i < size())
+  if (i < static_cast<int>(size()))
   {
     select(m_shapes[i]);
   }
diff --git a/Code/Mantid/MantidPlot/src/Mantid/InstrumentWidget/Shape2DCollection.h b/Code/Mantid/MantidPlot/src/Mantid/InstrumentWidget/Shape2DCollection.h
index ac9486f64a8f4e78572ab82965ee2445829890c0..fb80e38b37709b1340aebbd078dbc278fe7a05ca 100644
--- a/Code/Mantid/MantidPlot/src/Mantid/InstrumentWidget/Shape2DCollection.h
+++ b/Code/Mantid/MantidPlot/src/Mantid/InstrumentWidget/Shape2DCollection.h
@@ -39,7 +39,7 @@ public:
   void clear();
   bool isEmpty()const{return m_shapes.isEmpty();}
   size_t size()const {return static_cast<size_t>(m_shapes.size());}
-  void select(size_t i);
+  void select(int i);
 
   QRectF getCurrentBoundingRect()const;
   void setCurrentBoundingRect(const QRectF& rect);