diff --git a/src/rtoarmadillo.cpp b/src/rtoarmadillo.cpp
index e8bfe42..25f7661 100644
--- a/src/rtoarmadillo.cpp
+++ b/src/rtoarmadillo.cpp
@@ -556,8 +556,8 @@ arma::cube acf(arma::mat& x, int lagmax = 0, bool cor = true, bool demean = true
         
         for(int i = 0; i < nobs-lag; i++){
           
-          if(arma::is_finite(x[i + lag + nobs*u]) &&
-             arma::is_finite(x[i + nobs*v])) {
+          if(std::isfinite(x[i + lag + nobs*u]) &&
+             std::isfinite(x[i + nobs*v])) {
             nu++;
             sum += x[i + lag + nobs*u] * x[i + nobs*v];
           }
@@ -610,4 +610,4 @@ arma::cube acf(arma::mat& x, int lagmax = 0, bool cor = true, bool demean = true
   return acf;
 }
 
-/* ------------------ End R to Armadillo Functions ----------------------- */
\ No newline at end of file
+/* ------------------ End R to Armadillo Functions ----------------------- */