diff --git a/src/gpu/GridGenerator/grid/GridImp.cu b/src/gpu/GridGenerator/grid/GridImp.cu
index bbf0d4919c291422ce8f7309d93c039d3699a1b2..5ba3513d82b23edaf637932fb26ba00fbbf671ad 100644
--- a/src/gpu/GridGenerator/grid/GridImp.cu
+++ b/src/gpu/GridGenerator/grid/GridImp.cu
@@ -860,16 +860,15 @@ CUDA_HOST void GridImp::updateSparseIndices()
 
 CUDA_HOST void GridImp::findFluidNodeIndices() 
 {
-    // auf Basis von getNodeValues und updateSparseIndices
     for (uint index = 0; index < size; index++) {
-        uint sparseIndex = sparseIndices[index];
+        int sparseIndex = sparseIndices[index];
         if (sparseIndex == -1)
             continue;
 
         if (this->field.isFluid(index))
             fluidNodeIndices.push_back(sparseIndex);            
     }
-    numberOfFluidNodes = fluidNodeIndices.size();
+    numberOfFluidNodes = (uint) fluidNodeIndices.size();
 }
 
 HOSTDEVICE void GridImp::setNeighborIndices(uint index)
diff --git a/src/gpu/GridGenerator/grid/GridImp.h b/src/gpu/GridGenerator/grid/GridImp.h
index 06dc501e210ce198903eed2661bdd917c8f30e14..59569809348cda4e702bc59ae38eca871195c9b8 100644
--- a/src/gpu/GridGenerator/grid/GridImp.h
+++ b/src/gpu/GridGenerator/grid/GridImp.h
@@ -318,7 +318,7 @@ public:
 
     void findFluidNodeIndices() override;
     uint getNumberOfFluidNodes() const override;
-    CUDA_HOST void getFluidNodeIndices(uint *fluidNodeIndices) const;
+    CUDA_HOST void getFluidNodeIndices(uint *fluidNodeIndices) const override;
 
 
 public: