diff --git a/Applications/DataExplorer/DataView/DiagramView/DiagramList.cpp b/Applications/DataExplorer/DataView/DiagramView/DiagramList.cpp
index 8bf4aafd5d9b7d25f0aed93d87a9e285bef1ec06..69c4ac7bf98569e59277f4acde7a5226c1494200 100644
--- a/Applications/DataExplorer/DataView/DiagramView/DiagramList.cpp
+++ b/Applications/DataExplorer/DataView/DiagramView/DiagramList.cpp
@@ -344,7 +344,7 @@ void DiagramList::setList(std::vector<std::pair<float, float>> const& coords)
     update();
 }
 
-std::size_t DiagramList::size()
+std::size_t DiagramList::size() const
 {
     if (!(_coords.empty()))
         return _coords.size();
diff --git a/Applications/DataExplorer/DataView/DiagramView/DiagramList.h b/Applications/DataExplorer/DataView/DiagramView/DiagramList.h
index 25056016fe80276c0e002d15da14f5764275a9cb..66c43bd065e6ca57563ef0a91f61d8d92a40a3cc 100644
--- a/Applications/DataExplorer/DataView/DiagramView/DiagramList.h
+++ b/Applications/DataExplorer/DataView/DiagramView/DiagramList.h
@@ -141,7 +141,7 @@ public:
     void setYUnit(QString unit) { _yUnit = unit; }
 
     /// Returns the number of data points.
-    std::size_t size();
+    std::size_t size() const;
 
     /// Returns the width of the bounding box of all data points within the list.
     double width() const { return _maxX - _minX; }