diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index ca6b1501d1..1e6d8189c9 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -302,8 +302,10 @@ goodm:
 	get_tls(CX)		// Set G in TLS
 	MOVQ	R14, g(CX)
 	MOVQ	(g_sched+gobuf_sp)(R14), SP	// sp = g0.sched.sp
+	PUSHQ	AX	// open up space for fn's arg spill slot
 	MOVQ	0(DX), R12
 	CALL	R12		// fn(g)
+	POPQ	AX
 	JMP	runtime·badmcall2(SB)
 	RET
 #else