diff --git a/libexec/rtld-elf/amd64/rtld_machdep.h b/libexec/rtld-elf/amd64/rtld_machdep.h
index 91da22dabec..0fb431b9ad9 100644
--- a/libexec/rtld-elf/amd64/rtld_machdep.h
+++ b/libexec/rtld-elf/amd64/rtld_machdep.h
@@ -32,6 +32,8 @@
 #include <sys/types.h>
 #include <machine/atomic.h>
 
+#define	CACHE_LINE_SIZE		64
+
 struct Struct_Obj_Entry;
 
 /* Return the address of the .dynamic section in the dynamic linker. */