diff --git a/src/cmd/compile/internal/amd64/prog.go b/src/cmd/compile/internal/amd64/prog.go
index ae8f525..649b706 100644
--- a/src/cmd/compile/internal/amd64/prog.go
+++ b/src/cmd/compile/internal/amd64/prog.go
@@ -226,7 +226,7 @@
 	x86.ASTOSL:    {Flags: gc.OK, Reguse: AX | DI, Regset: DI},
 	x86.ASTOSQ:    {Flags: gc.OK, Reguse: AX | DI, Regset: DI},
 	x86.ASTOSW:    {Flags: gc.OK, Reguse: AX | DI, Regset: DI},
-	obj.ADUFFZERO: {Flags: gc.OK, Reguse: AX | DI, Regset: DI},
+	obj.ADUFFZERO: {Flags: gc.OK, Reguse: X0 | DI, Regset: DI},
 	x86.ASUBB:     {Flags: gc.SizeB | gc.LeftRead | RightRdwr | gc.SetCarry},
 	x86.ASUBL:     {Flags: gc.SizeL | gc.LeftRead | RightRdwr | gc.SetCarry},
 	x86.ASUBQ:     {Flags: gc.SizeQ | gc.LeftRead | RightRdwr | gc.SetCarry},