diff --git a/README.md b/README.md
index 2680175..6f8ad28 100644
--- a/README.md
+++ b/README.md
@@ -61,7 +61,7 @@ Usage:
 
 Flags:
 INPUT:
-   -a, -asn string[]     target asn to lookup, example: -a AS5650
+   -a, -asn string[]     target asn to lookup, example: -a AS5650, -a 5650
    -i, -ip string[]      target ip to lookup, example: -i 100.19.12.21, -i 2a10:ad40::
    -d, -domain string[]  target domain to lookup, example: -d google.com, -d facebook.com
    -org string[]         target organization to lookup, example: -org GOOGLE
diff --git a/runner/options.go b/runner/options.go
index 239004e..d13a899 100644
--- a/runner/options.go
+++ b/runner/options.go
@@ -4,7 +4,6 @@ import (
 	"errors"
 	"io"
 	"os"
-	"strings"
 
 	asnmap "github.com/projectdiscovery/asnmap/libs"
 	"github.com/projectdiscovery/goflags"
@@ -77,8 +76,8 @@ func (options *Options) validateOptions() error {
 	// validate asn input
 	if options.Asn != nil {
 		for _, asn := range options.Asn {
-			if !strings.HasPrefix(strings.ToUpper(asn), "AS") {
-				return errors.New("invalid ASN given. it should start with prefix 'AS', example : AS14421")
+			if t := asnmap.IdentifyInput(asn); t != asnmap.ASN && t != asnmap.ASNID {
+				return errors.New("invalid ASN given, example: AS14421 or 14421")
 			}
 		}
 	}
@@ -93,7 +92,7 @@ func ParseOptions() *Options {
 
 	// Input
 	flagSet.CreateGroup("input", "Input",
-		flagSet.StringSliceVarP(&options.Asn, "asn", "a", nil, "target asn to lookup, example: -a AS5650", goflags.FileNormalizedStringSliceOptions),
+		flagSet.StringSliceVarP(&options.Asn, "asn", "a", nil, "target asn to lookup, example: -a AS5650, -a 5650", goflags.FileNormalizedStringSliceOptions),
 		flagSet.StringSliceVarP(&options.Ip, "ip", "i", nil, "target ip to lookup, example: -i 100.19.12.21, -i 2a10:ad40:: ", goflags.FileNormalizedStringSliceOptions),
 		flagSet.StringSliceVarP(&options.Domain, "domain", "d", nil, "target domain to lookup, example: -d google.com, -d facebook.com", goflags.FileNormalizedStringSliceOptions),
 		flagSet.StringSliceVar(&options.Org, "org", nil, "target organization to lookup, example: -org GOOGLE", goflags.StringSliceOptions),
diff --git a/runner/options_test.go b/runner/options_test.go
new file mode 100644
index 0000000..1f32025
--- /dev/null
+++ b/runner/options_test.go
@@ -0,0 +1,18 @@
+package runner
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestValidateASNInput(t *testing.T) {
+	for _, asn := range []string{"AS13335", "as13335", "13335"} {
+		options := &Options{Asn: []string{asn}}
+		require.NoError(t, options.validateOptions(), asn)
+	}
+	for _, asn := range []string{"ASX", "google", "AS"} {
+		options := &Options{Asn: []string{asn}}
+		require.Error(t, options.validateOptions(), asn)
+	}
+}