diff --git a/basis/cpu/x86/64/64.factor b/basis/cpu/x86/64/64.factor
index 07ee01270a..fec3f453ae 100644
--- a/basis/cpu/x86/64/64.factor
+++ b/basis/cpu/x86/64/64.factor
@@ -11,7 +11,7 @@ IN: cpu.x86.64
 
 M: x86.64 machine-registers
     {
-        { int-regs { RAX RCX RDX RBP RSI RDI R8 R9 R10 R11 R12 R13 } }
+        { int-regs { RAX RCX RDX RBX RBP RSI RDI R8 R9 R10 R11 R12 R13 } }
         { double-float-regs {
             XMM0 XMM1 XMM2 XMM3 XMM4 XMM5 XMM6 XMM7
             XMM8 XMM9 XMM10 XMM11 XMM12 XMM13 XMM14 XMM15