diff --git a/.github/workflows/test_s390x.yaml b/.github/workflows/test_s390x.yaml
new file mode 100644
index 0000000..444e641
--- /dev/null
+++ b/.github/workflows/test_s390x.yaml
@@ -0,0 +1,36 @@
+# This workflow will build a golang project
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-go
+
+name: s390x-qemu
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+
+  test:
+    strategy:
+      matrix:
+        go-version: [1.19.x]
+        arch: [s390x]  
+    runs-on: ubuntu-latest
+    steps:
+    - name: Set up Go
+      uses: actions/setup-go@v5
+      with:
+        go-version: ${{ matrix.go-version }}
+
+    - name: Set up QEMU
+      uses: docker/setup-qemu-action@v3
+
+    - name: Check out code
+      uses: actions/checkout@v4
+
+    - name: Test bigmod
+      run: go test -v -short ./internal/bigmod/...
+ 
+    - name: Test subtle
+      run: go test -v -short ./internal/subtle/...
diff --git a/internal/sm2ec/p256_asm_table_test.go b/internal/sm2ec/p256_asm_table_test.go
index 1383bc1..9ce2247 100644
--- a/internal/sm2ec/p256_asm_table_test.go
+++ b/internal/sm2ec/p256_asm_table_test.go
@@ -1,4 +1,4 @@
-//go:build (amd64 && !purego && !plugin) || (arm64 && !purego)
+//go:build !purego && (amd64 || arm64)
 
 package sm2ec
 
diff --git a/internal/subtle/xor_generic.go b/internal/subtle/xor_generic.go
index e9db8d8..18dafd0 100644
--- a/internal/subtle/xor_generic.go
+++ b/internal/subtle/xor_generic.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.
 //
-//go:build purego || !(amd64 || arm64)
+//go:build purego || !(amd64 || arm64 || s390x)
 
 package subtle
 
diff --git a/internal/subtle/xor_s390x.go b/internal/subtle/xor_s390x.go
new file mode 100644
index 0000000..6fbacf9
--- /dev/null
+++ b/internal/subtle/xor_s390x.go
@@ -0,0 +1,10 @@
+// Copyright 2018 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.
+//
+//go:build !purego
+
+package subtle
+
+//go:noescape
+func xorBytes(dst, a, b *byte, n int)
diff --git a/internal/subtle/xor_s390x.s b/internal/subtle/xor_s390x.s
new file mode 100644
index 0000000..0e3f633
--- /dev/null
+++ b/internal/subtle/xor_s390x.s
@@ -0,0 +1,36 @@
+// Copyright 2016 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.
+
+//go:build !purego
+
+#include "textflag.h"
+
+// func xorBytes(dst, a, b *byte, n int)
+TEXT ·xorBytes(SB),NOSPLIT,$0-32
+	MOVD	dst+0(FP), R1
+	MOVD	a+8(FP), R2
+	MOVD	b+16(FP), R3
+	MOVD	n+24(FP), R4
+
+	MOVD	$0, R5
+	CMPBLT	R4, $8, tail
+loop:
+	MOVD	0(R2)(R5*1), R7
+	MOVD	0(R3)(R5*1), R8
+	XOR	R7, R8
+	MOVD	R8, 0(R1)(R5*1)
+	LAY	8(R5), R5
+	SUB	$8, R4
+	CMPBGE	R4, $8, loop
+tail:
+	CMPBEQ	R4, $0, done
+	MOVB	0(R2)(R5*1), R7
+	MOVB	0(R3)(R5*1), R8
+	XOR	R7, R8
+	MOVB	R8, 0(R1)(R5*1)
+	LAY	1(R5), R5
+	SUB	$1, R4
+	BR	tail
+done:
+	RET