diff --git a/tengo.go b/tengo.go
index b2a6acc..037bb06 100644
--- a/tengo.go
+++ b/tengo.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"context"
 	"bytes"
+	"strconv"
 )
 
 type Script = tengo.Script
@@ -162,7 +163,9 @@ func (pp *Tengo) Eval(
 				bts, ok := tengo.ToByteSlice(o)
 				if !ok {
 					return nil, tengo.ErrInvalidArgumentType{
+						Name: strconv.Itoa(i),
 						Expected: "string/bytes",
+						Found: o.TypeName(),
 					}
 				}
 				bt[i] = bts