diff --git a/reference/barrier/barrier/arrive.md b/reference/barrier/barrier/arrive.md
index 6af0b912ce..e98ab098ab 100644
--- a/reference/barrier/barrier/arrive.md
+++ b/reference/barrier/barrier/arrive.md
@@ -47,6 +47,7 @@ arrival_token arrive(ptrdiff_t update = 1); // (1) C++26
 #include <barrier>
 #include <chrono>
 #include <iostream>
+#include <mutex>
 #include <thread>
 #include <utility>
 
diff --git a/reference/barrier/barrier/arrive_and_drop.md b/reference/barrier/barrier/arrive_and_drop.md
index 8c54f1e472..fefb63d5c6 100644
--- a/reference/barrier/barrier/arrive_and_drop.md
+++ b/reference/barrier/barrier/arrive_and_drop.md
@@ -43,6 +43,7 @@ void arrive_and_drop();
 #include <barrier>
 #include <chrono>
 #include <iostream>
+#include <mutex>
 #include <thread>
 #include <utility>
 
diff --git a/reference/barrier/barrier/arrive_and_wait.md b/reference/barrier/barrier/arrive_and_wait.md
index 80259d5523..93abaf94f4 100644
--- a/reference/barrier/barrier/arrive_and_wait.md
+++ b/reference/barrier/barrier/arrive_and_wait.md
@@ -34,6 +34,7 @@ void arrive_and_wait();
 #include <barrier>
 #include <chrono>
 #include <iostream>
+#include <mutex>
 #include <thread>
 #include <utility>
 
diff --git a/reference/barrier/barrier/wait.md b/reference/barrier/barrier/wait.md
index 1f78e962a3..66905bb73a 100644
--- a/reference/barrier/barrier/wait.md
+++ b/reference/barrier/barrier/wait.md
@@ -38,6 +38,7 @@ void wait(arrival_token&& arrival) const;
 #include <barrier>
 #include <chrono>
 #include <iostream>
+#include <mutex>
 #include <thread>
 #include <utility>