diff --git a/src/Charts/Aerolab.cpp b/src/Charts/Aerolab.cpp
index 84847b113..97b6f5437 100644
--- a/src/Charts/Aerolab.cpp
+++ b/src/Charts/Aerolab.cpp
@@ -782,7 +782,7 @@ QString Aerolab::estimateCdACrr(RideItem *rideItem)
         const RideFileDataPresent *dataPresent = ride->areDataPresent();
         if(( dataPresent->alt || constantAlt )  && dataPresent->watts) {
             double dt = ride->recIntSecs();
-            int npoints = ride->dataPoints().size();
+            int npoints = ride->dataPoints().size() + 1;
 #ifdef Q_CC_MSVC
             double* X1 = new double[npoints];
             double* X2 = new double[npoints];