diff --git a/x86_64/README b/x86_64/README
index 95db7feeee335d0dd4a00dfb46e034141ea7ec76..11c2be1561e21dc70388c21688a2baef523a3187 100644
--- a/x86_64/README
+++ b/x86_64/README
@@ -1,7 +1,7 @@
 ABI, according to http://www.x86-64.org/documentation/abi-0.99.pdf:
 
 Up to 6 integer and pointer arguments are passed in registers. Nine
-registers, %rax, %rcx, %rdx, %rsi, %rdi and %r8-%r12 can be used
+registers, %rax, %rcx, %rdx, %rsi, %rdi and %r8-%r11 can be used
 freely. Integers and pointers are returned in %rax.
 
 Registers	May be		Argument