diff --git a/Code/Mantid/Framework/MDAlgorithms/src/LoadMD.cpp b/Code/Mantid/Framework/MDAlgorithms/src/LoadMD.cpp
index 5b5d3b02c1d2..e9736c335496 100644
--- a/Code/Mantid/Framework/MDAlgorithms/src/LoadMD.cpp
+++ b/Code/Mantid/Framework/MDAlgorithms/src/LoadMD.cpp
@@ -366,7 +366,10 @@ namespace Mantid
           if(!box)continue;
 
           if(BoxEventIndex[2*i+1]>0) // Load in memory NOT using the file as the back-end,
+          {
+            boxTree[i]->reserveMemoryForLoad(BoxEventIndex[2*i+1]);
             boxTree[i]->loadAndAddFrom(loader.get(),BoxEventIndex[2*i],static_cast<size_t>(BoxEventIndex[2*i+1]));
+          }
 
         }
         loader->closeFile();