diff --git a/Framework/Algorithms/inc/MantidAlgorithms/ExtractSpectra.h b/Framework/Algorithms/inc/MantidAlgorithms/ExtractSpectra.h
index 60f9e65fc4f674b2fba6147f57b71c5542ed5d23..eda7d0939fa56808b607aca9dd59aba0359a3232 100644
--- a/Framework/Algorithms/inc/MantidAlgorithms/ExtractSpectra.h
+++ b/Framework/Algorithms/inc/MantidAlgorithms/ExtractSpectra.h
@@ -47,8 +47,8 @@ private:
   void execEvent();
 
   void checkProperties();
-  std::size_t getXMin(const int wsIndex = 0);
-  std::size_t getXMax(const int wsIndex = 0);
+  std::size_t getXMin(const size_t wsIndex = 0);
+  std::size_t getXMax(const size_t wsIndex = 0);
   void cropRagged(API::MatrixWorkspace_sptr outputWorkspace, int inIndex,
                   int outIndex);
 
@@ -72,4 +72,4 @@ private:
 } // namespace Algorithms
 } // namespace Mantid
 
-#endif /* MANTID_ALGORITHMS_EXTRACTSPECTRA_H_ */
\ No newline at end of file
+#endif /* MANTID_ALGORITHMS_EXTRACTSPECTRA_H_ */
diff --git a/Framework/Algorithms/src/ExtractSpectra.cpp b/Framework/Algorithms/src/ExtractSpectra.cpp
index 38661d69145baa798d8afe15df8a1289c19ff077..216e46bc3a6aee87acee4e45b7d6fe29d9b7df27 100644
--- a/Framework/Algorithms/src/ExtractSpectra.cpp
+++ b/Framework/Algorithms/src/ExtractSpectra.cpp
@@ -377,11 +377,12 @@ void ExtractSpectra::checkProperties() {
     m_workspaceIndexList = getProperty("WorkspaceIndexList");
 
     if (m_workspaceIndexList.empty()) {
-      int minSpec = getProperty("StartWorkspaceIndex");
-      const int numberOfSpectra =
-          static_cast<int>(m_inputWorkspace->getNumberHistograms());
-      int maxSpec = getProperty("EndWorkspaceIndex");
-      if (isEmpty(maxSpec))
+      int minSpec_i = getProperty("StartWorkspaceIndex");
+      size_t minSpec = static_cast<size_t>(minSpec_i);
+      const size_t numberOfSpectra = m_inputWorkspace->getNumberHistograms();
+      int maxSpec_i = getProperty("EndWorkspaceIndex");
+      size_t maxSpec = static_cast<size_t>(maxSpec_i);
+      if (isEmpty(maxSpec_i))
         maxSpec = numberOfSpectra - 1;
 
       // Check 'StartSpectrum' is in range 0-numberOfSpectra
@@ -409,7 +410,7 @@ void ExtractSpectra::checkProperties() {
   }
 
   // get the x-range from the used spectra
-  int spectrumIndex = 0; // default is just look at the initial spectrum
+  size_t spectrumIndex = 0; // default is just look at the initial spectrum
   if (!m_workspaceIndexList.empty())
     spectrumIndex =
         m_workspaceIndexList.front(); // or the first one being extracted
@@ -441,7 +442,7 @@ void ExtractSpectra::checkProperties() {
  *  @param  wsIndex The workspace index to check (default 0).
  *  @return The X index corresponding to the XMin value.
  */
-size_t ExtractSpectra::getXMin(const int wsIndex) {
+size_t ExtractSpectra::getXMin(const size_t wsIndex) {
   double minX_val = getProperty("XMin");
   size_t xIndex = 0;
   if (!isEmpty(minX_val)) { // A value has been passed to the algorithm, check
@@ -468,7 +469,7 @@ size_t ExtractSpectra::getXMin(const int wsIndex) {
  *  @param  wsIndex The workspace index to check (default 0).
  *  @return The X index corresponding to the XMax value.
  */
-size_t ExtractSpectra::getXMax(const int wsIndex) {
+size_t ExtractSpectra::getXMax(const size_t wsIndex) {
   const auto &X = m_inputWorkspace->x(wsIndex);
   size_t xIndex = X.size();
   // get the value that the user entered if they entered one at all