diff --git a/ApplicationLibCode/ProjectDataModel/CellFilters/RimUserDefinedIndexFilter.cpp b/ApplicationLibCode/ProjectDataModel/CellFilters/RimUserDefinedIndexFilter.cpp
index a9941fed6e..c11f58f2ef 100644
--- a/ApplicationLibCode/ProjectDataModel/CellFilters/RimUserDefinedIndexFilter.cpp
+++ b/ApplicationLibCode/ProjectDataModel/CellFilters/RimUserDefinedIndexFilter.cpp
@@ -101,7 +101,7 @@ void RimUserDefinedIndexFilter::updateCellIndexFilter( cvf::UByteArray* includeV
 {
     if ( gridIndex != m_gridIndex() ) return;
 
-    const auto filterSize = includeVisibility->size();
+    const auto filterSize = (int)includeVisibility->size();
 
     if ( m_filterMode == FilterModeType::INCLUDE )
     {