diff --git a/include/otbNDVITimeSeriesFunctor.h b/include/otbNDVITimeSeriesFunctor.h
index e35f9d9f76e6673805f36a47d0505f136d3c7096..c5c19b5268153ad3af4ee982d4c986e4e715c2cf 100644
--- a/include/otbNDVITimeSeriesFunctor.h
+++ b/include/otbNDVITimeSeriesFunctor.h
@@ -284,7 +284,7 @@ inline TOutputPixel operator ()(const TInputPixel& input) const
 
   // Compute amplitude
   int lastYear = dates[dates.size()-1].year;
-  for (unsigned int i = 0 ; i < lastYear - firstYear +1 ; i++ )
+  for (int i = 0 ; i < lastYear - firstYear +1 ; i++ )
     {
     if (minimums[i] != this->GetInputNoDataValue() && maximums[i] != this->GetInputNoDataValue())
       {