diff --git a/splinterpolator.h b/splinterpolator.h
index 7578549082ccbb0f1de62a93ae2c82099c932168..5a33a5dff63b02eac2e5e1fc7ef016699fcb34b1 100644
--- a/splinterpolator.h
+++ b/splinterpolator.h
@@ -644,7 +644,7 @@ double Splinterpolator<T>::value_and_derivatives_at(const double       *coord,
 						    double             *dval) 
 const
 {
-  if (should_be_zero(coord)) { memset(dval,n_nonzero(deriv)*sizeof(double),0); return(0.0); }
+  if (should_be_zero(coord)) { memset(dval,0,n_nonzero(deriv)*sizeof(double)); return(0.0); }
 
   double       iwgt[8], jwgt[8], kwgt[8], lwgt[8], mwgt[8];
   double       *wgts[] = {iwgt, jwgt, kwgt, lwgt, mwgt};