diff --git a/db/index.test.ts b/db/index.test.ts
index 18314d3..d89d30e 100644
--- a/db/index.test.ts
+++ b/db/index.test.ts
@@ -8,24 +8,47 @@ describe("db connection", () => {
 
   it("creates and caches the native connection lazily", async () => {
     const database = { sql: {} };
+    const getConnectionString = vi.fn(() => "postgres://app:secret@database.example/test");
     const getDatabase = vi.fn(() => database);
-    vi.doMock("@netlify/database", () => ({ getDatabase }));
+    vi.doMock("@netlify/database", () => ({ getConnectionString, getDatabase }));
 
     const mod = await import("./index");
+    expect(getConnectionString).not.toHaveBeenCalled();
     expect(getDatabase).not.toHaveBeenCalled();
 
     expect(mod.getDb()).toBe(database);
     expect(mod.getDb()).toBe(database);
+    expect(getConnectionString).toHaveBeenCalledOnce();
     expect(getDatabase).toHaveBeenCalledOnce();
+    expect(getDatabase).toHaveBeenCalledWith();
+  });
+
+  it("adds the username missing from Netlify's local Database URL", async () => {
+    const database = { sql: {} };
+    const getConnectionString = vi.fn(() => "postgres://localhost:5432/postgres");
+    const getDatabase = vi.fn(() => database);
+    vi.doMock("@netlify/database", () => ({ getConnectionString, getDatabase }));
+
+    const mod = await import("./index");
+
+    expect(mod.getDb()).toBe(database);
+    expect(mod.getDb()).toBe(database);
+    expect(getConnectionString).toHaveBeenCalledOnce();
+    expect(getDatabase).toHaveBeenCalledOnce();
+    expect(getDatabase).toHaveBeenCalledWith({
+      connectionString: "postgres://postgres@localhost:5432/postgres",
+    });
   });
 
   it("does not hide a missing Database configuration", async () => {
-    const getDatabase = vi.fn(() => {
+    const getConnectionString = vi.fn(() => {
       throw new Error("Database is not configured");
     });
-    vi.doMock("@netlify/database", () => ({ getDatabase }));
+    const getDatabase = vi.fn();
+    vi.doMock("@netlify/database", () => ({ getConnectionString, getDatabase }));
 
     const mod = await import("./index");
     expect(() => mod.getDb()).toThrow("Database is not configured");
+    expect(getDatabase).not.toHaveBeenCalled();
   });
 });
diff --git a/db/index.ts b/db/index.ts
index d0dd9b8..ef3503e 100644
--- a/db/index.ts
+++ b/db/index.ts
@@ -1,11 +1,26 @@
-import { getDatabase, type DatabaseConnection } from "@netlify/database";
+import { getConnectionString, getDatabase, type DatabaseConnection } from "@netlify/database";
 
 let connection: DatabaseConnection | undefined;
 
+const LOOPBACK_HOSTS = new Set(["localhost", "127.0.0.1", "[::1]"]);
+
+function createConnection(): DatabaseConnection {
+  const connectionString = getConnectionString();
+  const url = new URL(connectionString);
+
+  if (!url.username && LOOPBACK_HOSTS.has(url.hostname)) {
+    // XXX(serhalp): Remove once Netlify's local Database URL includes a username.
+    url.username = "postgres";
+    return getDatabase({ connectionString: url.toString() });
+  }
+
+  return getDatabase();
+}
+
 // Keep connection creation lazy. An audit can still run and stream its result
 // when Database has not been provisioned; only the final save then fails, and
 // audit-stream already reports that failure separately from the audit itself.
 export function getDb(): DatabaseConnection {
-  connection ??= getDatabase();
+  connection ??= createConnection();
   return connection;
 }