diff --git a/src/util/movinginterquartilemean.cpp b/src/util/movinginterquartilemean.cpp
index 582fba5a488..ee1142e9f6c 100644
--- a/src/util/movinginterquartilemean.cpp
+++ b/src/util/movinginterquartilemean.cpp
@@ -3,6 +3,7 @@
 #include <qlogging.h>
 
 #include <algorithm>
+#include <cstddef>
 #include <iterator>
 #include <numeric>
 
@@ -59,7 +60,7 @@ double MovingInterquartileMean::mean() {
     if (listSize <= 4) {
         m_dMean = simpleMean(m_list.cbegin(), m_list.cend());
     } else if (listSize % 4 == 0) {
-        int quartileSize = listSize / 4;
+        std::size_t quartileSize = listSize / 4;
         auto start = m_list.cbegin() + quartileSize;
         auto end = m_list.cend() - quartileSize;
         m_dMean = simpleMean(start, end);
@@ -67,13 +68,13 @@ double MovingInterquartileMean::mean() {
         // http://en.wikipedia.org/wiki/Interquartile_mean#Dataset_not_divisible_by_four
         double quartileSize = listSize / 4.0;
         double interQuartileRange = 2 * quartileSize;
-        int nFullValues = listSize - 2 * static_cast<int>(quartileSize) - 2;
+        std::size_t nFullValues = listSize - 2 * static_cast<std::size_t>(quartileSize) - 2;
         double quartileWeight = (interQuartileRange - nFullValues) / 2;
         auto it = m_list.begin();
-        std::advance(it, static_cast<int>(quartileSize));
+        std::advance(it, static_cast<std::size_t>(quartileSize));
         double d_sum = *it * quartileWeight;
         ++it;
-        for (int k = 0; k < nFullValues; ++k, ++it) {
+        for (std::size_t k = 0; k < nFullValues; ++k, ++it) {
             d_sum += *it;
         }
         d_sum += *it * quartileWeight;