diff --git a/book/en-us/07-thread.md b/book/en-us/07-thread.md
index 375e8de..a49caa4 100644
--- a/book/en-us/07-thread.md
+++ b/book/en-us/07-thread.md
@@ -41,6 +41,7 @@ RAII guarantees the exceptional security of the code while keeping the simplicit
 
 ```cpp
 #include <iostream>
+#include <mutex>
 #include <thread>
 
 int v = 1;
@@ -80,6 +81,7 @@ For instance:
 
 ```cpp
 #include <iostream>
+#include <mutex>
 #include <thread>
 
 int v = 1;
diff --git a/book/zh-cn/07-thread.md b/book/zh-cn/07-thread.md
index 4eef992..e498204 100644
--- a/book/zh-cn/07-thread.md
+++ b/book/zh-cn/07-thread.md
@@ -42,6 +42,7 @@ RAII 在不失代码简洁性的同时，很好的保证了代码的异常安全
 
 ```cpp
 #include <iostream>
+#include <mutex>
 #include <thread>
 
 int v = 1;
@@ -82,6 +83,7 @@ int main() {
 
 ```cpp
 #include <iostream>
+#include <mutex>
 #include <thread>
 
 int v = 1;
diff --git a/code/7/7.2.critical.section.a.cpp b/code/7/7.2.critical.section.a.cpp
index 374a3e3..168d8c4 100644
--- a/code/7/7.2.critical.section.a.cpp
+++ b/code/7/7.2.critical.section.a.cpp
@@ -8,6 +8,7 @@
 //
 
 #include <iostream>
+#include <mutex>
 #include <thread>
 
 int v = 1;
diff --git a/code/7/7.3.critical.section.b.cpp b/code/7/7.3.critical.section.b.cpp
index ad4439d..930cd19 100644
--- a/code/7/7.3.critical.section.b.cpp
+++ b/code/7/7.3.critical.section.b.cpp
@@ -8,6 +8,7 @@
 //
 
 #include <iostream>
+#include <mutex>
 #include <thread>
 
 int v = 1;