diff --git a/doc/samples/map_array.cpp b/doc/samples/map_array.cpp
index 5cdc37a4..31229d99 100644
--- a/doc/samples/map_array.cpp
+++ b/doc/samples/map_array.cpp
@@ -18,8 +18,9 @@
 
 int main () {
     using namespace boost::numeric::ublas;
-    map_array<int, double> a (3);
-    for (unsigned i = 0; i < a.size (); ++ i) {
+    map_array<int, double> a;
+    a.reserve (3);
+    for (unsigned i = 0; i < 3; ++ i) {
         a [i] = i;
         std::cout << a [i] << std::endl;
     }