diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go
index 03f657da8a..b30dab9fe3 100644
--- a/src/cmd/compile/internal/ssa/prove.go
+++ b/src/cmd/compile/internal/ssa/prove.go
@@ -1068,6 +1068,10 @@ func isNonNegative(v *Value) bool {
 		OpZeroExt8to64, OpZeroExt16to64, OpZeroExt32to64:
 		return true
 
+	case OpRsh64Ux64:
+		by := v.Args[1]
+		return by.Op == OpConst64 && by.AuxInt > 0
+
 	case OpRsh64x64:
 		return isNonNegative(v.Args[0])
 	}