diff --git a/.github/workflows/test_riscv64.yaml b/.github/workflows/test_riscv64.yaml
index 2fb0c05..8b540a0 100644
--- a/.github/workflows/test_riscv64.yaml
+++ b/.github/workflows/test_riscv64.yaml
@@ -14,7 +14,7 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.22.x]
+        go-version: [1.18.x]
         arch: [riscv64]  
     runs-on: ubuntu-latest
     steps:
diff --git a/internal/bigmod/nat_riscv64.s b/internal/bigmod/nat_riscv64.s
index 2a7678c..5995346 100644
--- a/internal/bigmod/nat_riscv64.s
+++ b/internal/bigmod/nat_riscv64.s
@@ -85,10 +85,10 @@ loop:
 	MOV	X16, 2*8(X5)	// z[2]
 	MOV	X19, 3*8(X5)	// z[3]
 
-	ADD	$32, X5
-	ADD	$32, X7
+	ADDI	$32, X5
+	ADDI	$32, X7
 
-	SUB	$4, X30
+	ADDI	$-4, X30
 	BNEZ	X30, loop
 
 done: