diff --git a/libc/kernel/uapi/linux/magic.h b/libc/kernel/uapi/linux/magic.h
index c4d698e..4d24726 100644
--- a/libc/kernel/uapi/linux/magic.h
+++ b/libc/kernel/uapi/linux/magic.h
@@ -90,4 +90,5 @@
 #define DMA_BUF_MAGIC 0x444d4142
 #define DEVMEM_MAGIC 0x454d444d
 #define SECRETMEM_MAGIC 0x5345434d
+#define PID_FS_MAGIC 0x50494446
 #endif