diff --git a/libc/platform/bionic/mte_kernel.h b/libc/platform/bionic/mte_kernel.h
index e8ef2a5..d81480a 100644
--- a/libc/platform/bionic/mte_kernel.h
+++ b/libc/platform/bionic/mte_kernel.h
@@ -54,4 +54,6 @@
 #define PTRACE_PEEKMTETAGS 33
 #define PTRACE_POKEMTETAGS 34
 
+#define NT_ARM_TAGGED_ADDR_CTRL 0x409
+
 #endif