diff --git a/Code/Mantid/MantidQt/CustomInterfaces/src/MultiDatasetFit/MultiDatasetFit.cpp b/Code/Mantid/MantidQt/CustomInterfaces/src/MultiDatasetFit/MultiDatasetFit.cpp
index a478bc070e00c670e557e29a0463c613a640b25f..6dd5e11ed2a24e36e1d980775bcd1c2c24c9b3bb 100644
--- a/Code/Mantid/MantidQt/CustomInterfaces/src/MultiDatasetFit/MultiDatasetFit.cpp
+++ b/Code/Mantid/MantidQt/CustomInterfaces/src/MultiDatasetFit/MultiDatasetFit.cpp
@@ -178,7 +178,7 @@ void MultiDatasetFit::fitSequential()
 
     m_fitOptionsBrowser->copyPropertiesToAlgorithm(*fit);
 
-    m_outputWorkspaceName = m_fitOptionsBrowser->getProperty("OutputWorkspace") + "_Workspaces";
+    m_outputWorkspaceName = m_fitOptionsBrowser->getProperty("OutputWorkspace").toStdString() + "_Workspaces";
 
     m_fitRunner.reset( new API::AlgorithmRunner() );
     connect( m_fitRunner.get(),SIGNAL(algorithmComplete(bool)), this, SLOT(finishFit(bool)), Qt::QueuedConnection );
@@ -343,7 +343,7 @@ void MultiDatasetFit::finishFit(bool error)
     {
       auto paramsWSName = m_fitOptionsBrowser->getProperty("OutputWorkspace").toStdString();
       if (!Mantid::API::AnalysisDataService::Instance().doesExist(paramsWSName)) return;
-      auto nSpectra = getNumberOfSpectra();
+      size_t nSpectra = getNumberOfSpectra();
       if (nSpectra == 0) return;
       fun = m_functionBrowser->getGlobalFunction();
       auto nParams = fun->nParams() / nSpectra;