diff --git a/nns/nns_contract.go b/nns/nns_contract.go
index 6ef39d1..38e2ae9 100644
--- a/nns/nns_contract.go
+++ b/nns/nns_contract.go
@@ -231,15 +231,20 @@ func IsAvailable(name string) bool {
 		}
 		return true
 	}
-	if parentExpired(ctx, fragments) {
-		panic("parent does not exist or is expired")
-	}
+	checkParentExists(ctx, fragments)
 	return storage.Get(ctx, append([]byte{prefixName}, getTokenKey([]byte(name))...)) == nil
 }
 
-// parentExpired returns true if any domain from fragments doesn't exist or is expired.
+// checkParentExists panics if any domain from fragments doesn't exist or is expired.
+func checkParentExists(ctx storage.Context, fragments []string) {
+	if dom := parentExpired(ctx, fragments); dom != "" {
+		panic("domain does not exist or is expired: " + dom)
+	}
+}
+
+// parentExpired returns domain from fragments that doesn't exist or is expired.
 // first denotes the deepest subdomain to check.
-func parentExpired(ctx storage.Context, fragments []string) bool {
+func parentExpired(ctx storage.Context, fragments []string) string {
 	now := int64(runtime.GetTime())
 	last := len(fragments) - 1
 	name := fragments[last]
@@ -249,14 +254,14 @@ func parentExpired(ctx storage.Context, fragments []string) bool {
 		}
 		nsBytes := storage.Get(ctx, append([]byte{prefixName}, getTokenKey([]byte(name))...))
 		if nsBytes == nil {
-			return true
+			return name
 		}
 		ns := std.Deserialize(nsBytes.([]byte)).(NameState)
 		if now >= ns.Expiration {
-			return true
+			return name
 		}
 	}
-	return false
+	return ""
 }
 
 // Register registers a new domain with the specified owner and name if it's available.
@@ -280,9 +285,8 @@ func Register(name string, owner interop.Hash160, email string, refresh, retry,
 		if tldBytes == nil {
 			panic("TLD not found")
 		}
-		if parentExpired(ctx, fragments) {
-			panic("one of the parent domains is not registered")
-		}
+		checkParentExists(ctx, fragments)
+
 		parentKey := getTokenKey([]byte(name[len(fragments[0])+1:]))
 		nsBytes := storage.Get(ctx, append([]byte{prefixName}, parentKey...))
 		ns := std.Deserialize(nsBytes.([]byte)).(NameState)
@@ -511,9 +515,7 @@ func getNameState(ctx storage.Context, tokenID []byte) NameState {
 	tokenKey := getTokenKey(tokenID)
 	ns := getNameStateWithKey(ctx, tokenKey)
 	fragments := std.StringSplit(string(tokenID), ".")
-	if parentExpired(ctx, fragments) {
-		panic("parent domain has expired")
-	}
+	checkParentExists(ctx, fragments)
 	return ns
 }
 
diff --git a/tests/nns_test.go b/tests/nns_test.go
index dc2621c..9cd16aa 100644
--- a/tests/nns_test.go
+++ b/tests/nns_test.go
@@ -167,7 +167,7 @@ func TestNNSRegisterMulti(t *testing.T) {
 
 	c1 := c.WithSigners(acc)
 	t.Run("parent domain is missing", func(t *testing.T) {
-		msg := "one of the parent domains is not registered"
+		msg := "domain does not exist or is expired: fs.neo.com"
 		args[0] = "testnet.fs.neo.com"
 		c1.InvokeFail(t, msg, "register", args...)
 	})
@@ -342,6 +342,8 @@ func TestNNSIsAvailable(t *testing.T) {
 
 	acc := c.NewAccount(t)
 	c1 := c.WithSigners(c.Committee, acc)
+
+	c1.InvokeFail(t, "domain does not exist or is expired: domain.com", "isAvailable", "dom.domain.com")
 	c1.Invoke(t, true, "register",
 		"domain.com", acc.ScriptHash(),
 		"myemail@frostfs.info", refresh, retry, expire, ttl)
@@ -349,7 +351,7 @@ func TestNNSIsAvailable(t *testing.T) {
 	c.Invoke(t, false, "isAvailable", "domain.com")
 
 	c.Invoke(t, true, "isAvailable", "dom.domain.com")
-	c.InvokeFail(t, "parent does not exist or is expired", "isAvailable", "dom.dom.domain.com")
+	c.InvokeFail(t, "domain does not exist or is expired: dom.domain.com", "isAvailable", "dom.dom.domain.com")
 
 	c1.Invoke(t, true, "register",
 		"dom.domain.com", acc.ScriptHash(),