--- branches/development/src/utils/Grid3d.hpp	2011/11/22 20:38:56	1665
+++ trunk/src/utils/Grid3d.hpp	2012/08/31 17:29:35	1792
@@ -99,8 +99,8 @@ namespace OpenMD {
   private:
     
     int isValidGrid(unsigned int i, unsigned int j, unsigned int k) const {
-      int index = i * dim2_*dim3_ + j * dim3_ + k;
-      return index < data_.size() ? index : -1;
+      unsigned int index = i * dim2_*dim3_ + j * dim3_ + k;
+      return index < data_.size() ? int(index) : -1;
     };
     
     unsigned int dim1_;