diff --git a/src/math/big/arith_decl.go b/src/math/big/arith_decl.go
index 53ab012988818baa69a9600dee57ecae36f0ce0c..41e592334c376ecc532bd5bf870c7fe89f3c12ab 100644
--- a/src/math/big/arith_decl.go
+++ b/src/math/big/arith_decl.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !math_big_pure_go,!riscv64
+// +build !math_big_pure_go
 
 package big
 
diff --git a/src/math/big/arith_decl_pure.go b/src/math/big/arith_decl_pure.go
index 4021a6d2994b723d4cd06e5e1a773408b0a2fe38..305f7ee03b42d8078fc43dc33a1a7b8f0c58f8b2 100644
--- a/src/math/big/arith_decl_pure.go
+++ b/src/math/big/arith_decl_pure.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build math_big_pure_go riscv64
+// +build math_big_pure_go
 
 package big
 
diff --git a/src/math/big/arith_riscv64.s b/src/math/big/arith_riscv64.s
new file mode 100644
index 0000000000000000000000000000000000000000..59065c3f7bac37cf6011b15dfd2838d739f450f5
--- /dev/null
+++ b/src/math/big/arith_riscv64.s
@@ -0,0 +1,51 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !math_big_pure_go,riscv64
+
+#include "textflag.h"
+
+// This file provides fast assembly versions for the elementary
+// arithmetic operations on vectors implemented in arith.go.
+
+// func mulWW(x, y Word) (z1, z0 Word)
+TEXT ·mulWW(SB),NOSPLIT,$0
+	MOV	x+0(FP), X5
+	MOV	y+8(FP), X6
+	MULHU	X5, X6, X7
+	MUL	X5, X6, X8
+	MOV	X7, z1+16(FP)
+	MOV	X8, z0+24(FP)
+	RET
+
+// func divWW(x1, x0, y Word) (q, r Word)
+TEXT ·divWW(SB),NOSPLIT,$0
+	JMP ·divWW_g(SB)		// riscv64 has no multiword division
+
+TEXT ·addVV(SB),NOSPLIT,$0
+	JMP ·addVV_g(SB)
+
+TEXT ·subVV(SB),NOSPLIT,$0
+	JMP ·subVV_g(SB)
+
+TEXT ·addVW(SB),NOSPLIT,$0
+	JMP ·addVW_g(SB)
+
+TEXT ·subVW(SB),NOSPLIT,$0
+	JMP ·subVW_g(SB)
+
+TEXT ·shlVU(SB),NOSPLIT,$0
+	JMP ·shlVU_g(SB)
+
+TEXT ·shrVU(SB),NOSPLIT,$0
+	JMP ·shrVU_g(SB)
+
+TEXT ·mulAddVWW(SB),NOSPLIT,$0
+	JMP ·mulAddVWW_g(SB)
+
+TEXT ·addMulVVW(SB),NOSPLIT,$0
+	JMP ·addMulVVW_g(SB)
+
+TEXT ·divWVW(SB),NOSPLIT,$0
+	JMP ·divWVW_g(SB)