1 files changed, 1 insertions, 0 deletions
diff --git a/doc/html/boost_asio/example/cpp11/executors/pipeline.cpp b/doc/html/boost_asio/example/cpp11/executors/pipeline.cpp
index 52b70cad56..9c2a778fee 100644
--- a/doc/html/boost_asio/example/cpp11/executors/pipeline.cpp
+++ b/doc/html/boost_asio/example/cpp11/executors/pipeline.cpp
@@ -11,6 +11,7 @@
 #include <queue>
 #include <thread>
 #include <vector>
+#include <cctype>
 
 using boost::asio::execution_context;
 using boost::asio::executor_binder;