diff --git a/cmd/oras/internal/option/spec.go b/cmd/oras/internal/option/spec.go
index 9d994ff02..ccbb204fb 100644
--- a/cmd/oras/internal/option/spec.go
+++ b/cmd/oras/internal/option/spec.go
@@ -71,7 +71,7 @@ func (opts *distributionSpec) Parse() error {
 		isApi := true
 		opts.referrersAPI = &isApi
 	default:
-		return fmt.Errorf("unknown image specification flag: %q", opts.specFlag)
+		return fmt.Errorf("unknown distribution specification flag: %q", opts.specFlag)
 	}
 	return nil
 }
diff --git a/test/e2e/suite/command/attach.go b/test/e2e/suite/command/attach.go
index e761a1a0e..54c35f6c3 100644
--- a/test/e2e/suite/command/attach.go
+++ b/test/e2e/suite/command/attach.go
@@ -60,6 +60,16 @@ var _ = Describe("ORAS beginners:", func() {
 			ORAS("attach", "--artifact-type", "oras.test", LayoutRef(root, foobar.Tag)).
 				ExpectFailure().MatchErrKeyWords("Error: no blob or manifest annotation are provided").Exec()
 		})
+
+		It("should fail if distribution spec is unkown", func() {
+			ORAS("attach", "--artifact-type", "oras.test", RegistryRef(Host, ImageRepo, foobar.Tag), "--distribution-spec", "???").
+				ExpectFailure().MatchErrKeyWords("unknown distribution specification flag").Exec()
+		})
+
+		It("should fail if image spec is unkown", func() {
+			ORAS("attach", "--artifact-type", "oras.test", RegistryRef(Host, ImageRepo, foobar.Tag), "--image-spec", "???").
+				ExpectFailure().MatchErrKeyWords("unknown image specification flag").Exec()
+		})
 	})
 })