diff --git a/src/gpu/GridGenerator/VelocitySetter/VelocitySetter.cu b/src/gpu/GridGenerator/VelocitySetter/VelocitySetter.cu
index faf1d95fd60252e47c70b7718d9b59986093c3ae..ade1087044381203d80171874df17fc8c1b33962 100644
--- a/src/gpu/GridGenerator/VelocitySetter/VelocitySetter.cu
+++ b/src/gpu/GridGenerator/VelocitySetter/VelocitySetter.cu
@@ -259,9 +259,9 @@ void VTKReader::fillArrays(std::vector<real>& coordsY, std::vector<real>& coords
         real posZ = coordsZ[i];
         bool foundNT = false, foundNB = false, foundST = false, foundSB = false, foundAll = false;
 
-        for(int level=this->fileCollection->files.size()-1; level>=0; level--) // go backwards to find finest nodes first
+        for(int level=(int)this->fileCollection->files.size()-1; level>=0; level--) // go backwards to find finest nodes first
         {
-            for(int fileId=0; fileId<this->fileCollection->files[level].size(); fileId++)
+            for(int fileId=0; fileId<(int)this->fileCollection->files[level].size(); fileId++)
             {
                 VTKFile file = this->fileCollection->files[level][fileId][0];
                 if(!file.inBoundingBox(posY, posZ, 0.0f)) continue;