diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 0135c76..1689e28 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -29,6 +29,7 @@
 
 extern struct pid_namespace init_pid_ns;
 
+#ifdef CONFIG_PID_NS
 static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
 {
 	if (ns != &init_pid_ns)
@@ -45,6 +46,28 @@
 		kref_put(&ns->kref, free_pid_ns);
 }
 
+#else /* !CONFIG_PID_NS */
+#include <linux/err.h>
+
+static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
+{
+	return ns;
+}
+
+static inline struct pid_namespace *
+copy_pid_ns(unsigned long flags, struct pid_namespace *ns)
+{
+	if (flags & CLONE_NEWPID)
+		ns = ERR_PTR(-EINVAL);
+	return ns;
+}
+
+static inline void put_pid_ns(struct pid_namespace *ns)
+{
+}
+
+#endif /* CONFIG_PID_NS */
+
 static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
 {
 	return tsk->nsproxy->pid_ns;