diff --git a/pkg/test/assembly_test.go b/pkg/test/assembly_test.go
index 69dfb53db..11d8272a1 100644
--- a/pkg/test/assembly_test.go
+++ b/pkg/test/assembly_test.go
@@ -19,6 +19,10 @@ import (
 	test_util "github.com/consensys/go-corset/pkg/test/util"
 )
 
+func Test_Asm_Add(t *testing.T) {
+	test_util.Check(t, false, "asm/add")
+}
+
 // Recusion
 //
 //	func Test_Asm_Byte(t *testing.T) {
diff --git a/pkg/util/word/big_endian.go b/pkg/util/word/big_endian.go
index ff0a80da1..037edd173 100644
--- a/pkg/util/word/big_endian.go
+++ b/pkg/util/word/big_endian.go
@@ -14,7 +14,6 @@ package word
 
 import (
 	"bytes"
-	"encoding/hex"
 	"hash/fnv"
 	"math/big"
 
@@ -109,11 +108,9 @@ func (p BigEndian) Bytes() []byte {
 }
 
 func (p BigEndian) String() string {
-	if len(p.bytes) == 0 {
-		return "0"
-	}
+	bi := p.AsBigInt()
 	//
-	return hex.EncodeToString(p.bytes)
+	return bi.String()
 }
 
 func trim(bytes []byte) []byte {
diff --git a/testdata/asm/add.accepts.bz2 b/testdata/asm/add.accepts.bz2
new file mode 100644
index 000000000..240f47cef
Binary files /dev/null and b/testdata/asm/add.accepts.bz2 differ
diff --git a/testdata/asm/add.zkasm b/testdata/asm/add.zkasm
new file mode 100644
index 000000000..f0d661980
--- /dev/null
+++ b/testdata/asm/add.zkasm
@@ -0,0 +1,15 @@
+fn add(inst u8, arg1 u256, arg2 u256) -> (res u256) {
+  var c u1
+  ;;
+  if inst == 0x01 goto insn_add
+  if inst == 0x03 goto insn_sub
+  ;; FIXME: support fail
+  res = 0
+  return
+insn_add:
+  c, res = arg1 + arg2
+  return
+insn_sub:
+  c, res = arg1 - arg2
+  return
+}