diff --git a/tools/testing/selftests/pid_namespace/pid_max.c b/tools/testing/selftests/pid_namespace/pid_max.c
index 51c414faabb0..96f274f0582b 100644
--- a/tools/testing/selftests/pid_namespace/pid_max.c
+++ b/tools/testing/selftests/pid_namespace/pid_max.c
@@ -10,6 +10,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <syscall.h>
+#include <sys/mount.h>
 #include <sys/wait.h>
 
 #include "../kselftest_harness.h"