diff --git a/service.go b/service.go
index 74fff66..9af31b2 100644
--- a/service.go
+++ b/service.go
@@ -199,26 +199,24 @@ func NewService(options ServiceOptions) *Service {
 		if mainchainURL == "" {
 			mainchainURL = strings.TrimSpace(options.HSDURL)
 		}
-		if mainchainURL != "" {
-			mainchainPassword := options.MainchainPassword
-			mainchainUsername := options.MainchainUsername
-			if strings.TrimSpace(options.MainchainURL) == "" {
+		mainchainPassword := options.MainchainPassword
+		mainchainUsername := options.MainchainUsername
+		if strings.TrimSpace(options.MainchainURL) == "" {
+			if mainchainPassword == "" {
+				mainchainPassword = options.HSDPassword
 				if mainchainPassword == "" {
-					mainchainPassword = options.HSDPassword
-					if mainchainPassword == "" {
-						mainchainPassword = options.HSDApiKey
-					}
-				}
-				if mainchainUsername == "" {
-					mainchainUsername = options.HSDUsername
+					mainchainPassword = options.HSDApiKey
 				}
 			}
-			mainchainClient = NewMainchainAliasClient(MainchainClientOptions{
-				URL:      mainchainURL,
-				Username: mainchainUsername,
-				Password: mainchainPassword,
-			})
+			if mainchainUsername == "" {
+				mainchainUsername = options.HSDUsername
+			}
 		}
+		mainchainClient = NewMainchainAliasClient(MainchainClientOptions{
+			URL:      mainchainURL,
+			Username: mainchainUsername,
+			Password: mainchainPassword,
+		})
 	}
 
 	cached := make(map[string]NameRecords, len(options.Records))
diff --git a/service_test.go b/service_test.go
index 5b25b8f..f45283c 100644
--- a/service_test.go
+++ b/service_test.go
@@ -1587,12 +1587,13 @@ func TestServiceDiscoverFromChainAliasesIgnoresMissingDiscoverers(t *testing.T)
 			},
 		},
 	})
+	service.mainchainAliasClient = nil
 	client := NewHSDClient(HSDClientOptions{
 		URL: server.URL,
 	})
 
 	if err := service.DiscoverFromChainAliases(context.Background(), client); err != nil {
-		t.Fatalf("expected no-op when no alias discoverer configured: %v", err)
+		t.Fatalf("expected no-op when no alias discoverer configured and no mainchain client: %v", err)
 	}
 
 	result, ok := service.Resolve("gateway.charon.lthn")
@@ -1623,9 +1624,10 @@ func TestServiceDiscoverAliasesReturnsNilWithoutDiscovererOrHSDClient(t *testing
 			},
 		},
 	})
+	service.mainchainAliasClient = nil
 
 	if err := service.DiscoverAliases(context.Background()); err != nil {
-		t.Fatalf("expected discover aliases to no-op without sources or HSD client: %v", err)
+		t.Fatalf("expected discover aliases to no-op without sources or HSD client when no explicit mainchain client: %v", err)
 	}
 
 	result, ok := service.Resolve("gateway.charon.lthn")
@@ -2675,6 +2677,19 @@ func TestServiceDiscoverAliasesFallsBackToMainchainAliasRPCUsingHSDURL(t *testin
 	}
 }
 
+func TestNewServiceBuildsMainchainAliasClientByDefault(t *testing.T) {
+	service := NewService(ServiceOptions{
+		Records: map[string]NameRecords{},
+	})
+
+	if service.mainchainAliasClient == nil {
+		t.Fatal("expected default mainchain alias client when none is provided")
+	}
+	if got := service.mainchainAliasClient.baseURL; got != "http://127.0.0.1:14037" {
+		t.Fatalf("expected fallback mainchain alias client URL %q, got %q", "http://127.0.0.1:14037", got)
+	}
+}
+
 func TestStringActionValueTrimsWhitespaceForRequiredArgument(t *testing.T) {
 	value, err := stringActionValue(map[string]any{
 		actionArgName: "  gateway.charon.lthn  ",