diff --git a/dune/contact/assemblers/largedeformationcoupling.cc b/dune/contact/assemblers/largedeformationcoupling.cc
index d5dc4fb20f4caba152248ed8297c779d8a8115ff..65f517be0cb22ac681da7126f67307b6d95ad5d8 100644
--- a/dune/contact/assemblers/largedeformationcoupling.cc
+++ b/dune/contact/assemblers/largedeformationcoupling.cc
@@ -838,7 +838,7 @@ void LargeDeformationCoupling<field_type, GridType0,GridType1>::setupIndexPatter
 
   const auto& indexSet0 = grid0_->leafIndexSet();
   const auto& indexSet1 = grid1_->leafIndexSet();
-  int size0{indexSet0.size(dim)},size1{indexSet1.size(dim)};
+  size_t size0(indexSet0.size(dim)),size1(indexSet1.size(dim));
 
   MatrixIndexSet nmIndices(nObstacles, size0);
   MatrixIndexSet mIndices(nObstacles, size1);