diff --git a/src/cmd/internal/obj/arm64/obj7.go b/src/cmd/internal/obj/arm64/obj7.go
index bed21dbe53..514991e340 100644
--- a/src/cmd/internal/obj/arm64/obj7.go
+++ b/src/cmd/internal/obj/arm64/obj7.go
@@ -107,55 +107,35 @@ func (c *ctxt7) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
 		p.From.Reg = REG_R1
 		p.Reg = REG_R2
 	} else {
-		// Such a large stack we need to protect against wraparound
-		// if SP is close to zero.
-		//	SP-stackguard+StackGuard < framesize + (StackGuard-StackSmall)
-		// The +StackGuard on both sides is required to keep the left side positive:
-		// SP is allowed to be slightly below stackguard. See stack.h.
-		//	CMP	$StackPreempt, R1
-		//	BEQ	label_of_call_to_morestack
-		//	ADD	$StackGuard, SP, R2
-		//	SUB	R1, R2
-		//	MOV	$(framesize+(StackGuard-StackSmall)), R3
-		//	CMP	R3, R2
-		p = obj.Appendp(p, c.newprog)
+		// Such a large stack we need to protect against underflow.
+		// The runtime guarantees SP > objabi.StackBig, but
+		// framesize is large enough that SP-framesize may
+		// underflow, causing a direct comparison with the
+		// stack guard to incorrectly succeed. We explicitly
+		// guard against underflow.
+		//
+		//	SUBS	$(framesize-StackSmall), SP, R2
+		//	// On underflow, jump to morestack
+		//	BLO	label_of_call_to_morestack
+		//	CMP	stackguard, R2
 
-		p.As = ACMP
+		p = obj.Appendp(p, c.newprog)
+		p.As = ASUBS
 		p.From.Type = obj.TYPE_CONST
-		p.From.Offset = objabi.StackPreempt
-		p.Reg = REG_R1
-
-		p = obj.Appendp(p, c.newprog)
-		q = p
-		p.As = ABEQ
-		p.To.Type = obj.TYPE_BRANCH
-
-		p = obj.Appendp(p, c.newprog)
-		p.As = AADD
-		p.From.Type = obj.TYPE_CONST
-		p.From.Offset = int64(objabi.StackGuard)
+		p.From.Offset = int64(framesize) - objabi.StackSmall
 		p.Reg = REGSP
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = REG_R2
 
 		p = obj.Appendp(p, c.newprog)
-		p.As = ASUB
-		p.From.Type = obj.TYPE_REG
-		p.From.Reg = REG_R1
-		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_R2
-
-		p = obj.Appendp(p, c.newprog)
-		p.As = AMOVD
-		p.From.Type = obj.TYPE_CONST
-		p.From.Offset = int64(framesize) + (int64(objabi.StackGuard) - objabi.StackSmall)
-		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_R3
+		q = p
+		p.As = ABLO
+		p.To.Type = obj.TYPE_BRANCH
 
 		p = obj.Appendp(p, c.newprog)
 		p.As = ACMP
 		p.From.Type = obj.TYPE_REG
-		p.From.Reg = REG_R3
+		p.From.Reg = REG_R1
 		p.Reg = REG_R2
 	}