diff --git a/.gitignore b/.gitignore
index e405ae2e..18813eb7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -42,3 +42,6 @@ tmpgen/
 
 # ReSharper/Rider user settings
 *.DotSettings.user
+
+# Local issue tracking
+tickerq_open_issues.md
diff --git a/src/TickerQ.EntityFrameworkCore/Customizer/TickerModelCustomizer.cs b/src/TickerQ.EntityFrameworkCore/Customizer/TickerModelCustomizer.cs
index dfb66b55..3a9964c0 100644
--- a/src/TickerQ.EntityFrameworkCore/Customizer/TickerModelCustomizer.cs
+++ b/src/TickerQ.EntityFrameworkCore/Customizer/TickerModelCustomizer.cs
@@ -16,7 +16,7 @@ public TickerModelCustomizer(ModelCustomizerDependencies dependencies)
 
         public override void Customize(ModelBuilder builder, DbContext context)
         {
-            var schema = context.GetService<TickerQEfCoreOptionBuilder<TTimeTicker, TCronTicker>>().Schema;
+            var schema = context.GetService<TickerQEfCoreOptionBuilder<TTimeTicker, TCronTicker>>()?.Schema ?? Constants.DefaultSchema;
 
             builder.ApplyConfiguration(new TimeTickerConfigurations<TTimeTicker>(schema));
             builder.ApplyConfiguration(new CronTickerConfigurations<TCronTicker>(schema));
diff --git a/src/TickerQ.EntityFrameworkCore/DbContextFactory/TickerQDbContext.cs b/src/TickerQ.EntityFrameworkCore/DbContextFactory/TickerQDbContext.cs
index 268d773f..7d05ba87 100644
--- a/src/TickerQ.EntityFrameworkCore/DbContextFactory/TickerQDbContext.cs
+++ b/src/TickerQ.EntityFrameworkCore/DbContextFactory/TickerQDbContext.cs
@@ -23,7 +23,7 @@ protected TickerQDbContext(DbContextOptions options) : base(options)
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
-        var schema = this.GetService<TickerQEfCoreOptionBuilder<TTimeTicker, TCronTicker>>().Schema;
+        var schema = this.GetService<TickerQEfCoreOptionBuilder<TTimeTicker, TCronTicker>>()?.Schema ?? Constants.DefaultSchema;
 
         modelBuilder.ApplyConfiguration(new TimeTickerConfigurations<TTimeTicker>(schema)); 
         modelBuilder.ApplyConfiguration(new CronTickerConfigurations<TCronTicker>(schema)); 
diff --git a/tests/TickerQ.EntityFrameworkCore.Tests/Infrastructure/DesignTimeDbContextTests.cs b/tests/TickerQ.EntityFrameworkCore.Tests/Infrastructure/DesignTimeDbContextTests.cs
new file mode 100644
index 00000000..c87ae940
--- /dev/null
+++ b/tests/TickerQ.EntityFrameworkCore.Tests/Infrastructure/DesignTimeDbContextTests.cs
@@ -0,0 +1,148 @@
+using Microsoft.Data.Sqlite;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.Extensions.DependencyInjection;
+using TickerQ.EntityFrameworkCore.Customizer;
+using TickerQ.EntityFrameworkCore.DbContextFactory;
+using TickerQ.Utilities.Entities;
+
+namespace TickerQ.EntityFrameworkCore.Tests.Infrastructure;
+
+/// <summary>
+/// Tests that TickerQDbContext and TickerModelCustomizer work at design-time
+/// when TickerQEfCoreOptionBuilder is not available in the service provider.
+/// Covers issue #457: design-time migrations fail with NullReferenceException.
+/// </summary>
+public class DesignTimeDbContextTests : IDisposable
+{
+    private readonly SqliteConnection _connection;
+
+    public DesignTimeDbContextTests()
+    {
+        _connection = new SqliteConnection("DataSource=:memory:");
+        _connection.Open();
+    }
+
+    public void Dispose() => _connection.Dispose();
+
+    #region TickerQDbContext — OnModelCreating without DI
+
+    [Fact]
+    public void OnModelCreating_WithoutOptionBuilder_UsesDefaultSchema()
+    {
+        // Simulate design-time: create DbContext without registering TickerQEfCoreOptionBuilder
+        var options = new DbContextOptionsBuilder<TickerQDbContext>()
+            .UseSqlite(_connection)
+            .Options;
+
+        using var context = new TickerQDbContext(options);
+
+        // OnModelCreating should not throw — it should fall back to Constants.DefaultSchema
+        var model = context.Model;
+
+        // Verify the tables use the default "ticker" schema
+        var timeTickerEntity = model.FindEntityType(typeof(TimeTickerEntity));
+        Assert.NotNull(timeTickerEntity);
+        Assert.Equal("ticker", timeTickerEntity.GetSchema());
+
+        var cronTickerEntity = model.FindEntityType(typeof(CronTickerEntity));
+        Assert.NotNull(cronTickerEntity);
+        Assert.Equal("ticker", cronTickerEntity.GetSchema());
+    }
+
+    [Fact]
+    public void OnModelCreating_WithOptionBuilder_UsesConfiguredSchema()
+    {
+        // Simulate runtime: TickerQEfCoreOptionBuilder is available with custom schema
+        var optionBuilder = new TickerQEfCoreOptionBuilder<TimeTickerEntity, CronTickerEntity>();
+        optionBuilder.SetSchema("custom_schema");
+
+        var services = new ServiceCollection();
+        services.AddSingleton(optionBuilder);
+        var serviceProvider = services.BuildServiceProvider();
+
+        var options = new DbContextOptionsBuilder<TickerQDbContext>()
+            .UseSqlite(_connection)
+            .UseApplicationServiceProvider(serviceProvider)
+            .Options;
+
+        using var context = new TickerQDbContext(options);
+        var model = context.Model;
+
+        var timeTickerEntity = model.FindEntityType(typeof(TimeTickerEntity));
+        Assert.NotNull(timeTickerEntity);
+        Assert.Equal("custom_schema", timeTickerEntity.GetSchema());
+    }
+
+    [Fact]
+    public void OnModelCreating_WithoutOptionBuilder_CanCreateDatabase()
+    {
+        // Verify the full design-time flow: create context → ensure created (simulates migration)
+        var options = new DbContextOptionsBuilder<TickerQDbContext>()
+            .UseSqlite(_connection)
+            .Options;
+
+        using var context = new TickerQDbContext(options);
+
+        // This exercises the full model building + DDL generation path
+        var created = context.Database.EnsureCreated();
+        Assert.True(created);
+    }
+
+    #endregion
+
+    #region TickerModelCustomizer — Customize without DI
+
+    [Fact]
+    public void TickerModelCustomizer_WithoutOptionBuilder_UsesDefaultSchema()
+    {
+        // Simulate design-time with UseApplicationDbContext path:
+        // TickerModelCustomizer replaces IModelCustomizer, but TickerQEfCoreOptionBuilder is missing
+        var options = new DbContextOptionsBuilder<CustomAppDbContext>()
+            .UseSqlite(_connection)
+            .ReplaceService<IModelCustomizer, TickerModelCustomizer<TimeTickerEntity, CronTickerEntity>>()
+            .Options;
+
+        using var context = new CustomAppDbContext(options);
+        var model = context.Model;
+
+        // TickerQ entities should be configured with default schema
+        var timeTickerEntity = model.FindEntityType(typeof(TimeTickerEntity));
+        Assert.NotNull(timeTickerEntity);
+        Assert.Equal("ticker", timeTickerEntity.GetSchema());
+    }
+
+    [Fact]
+    public void TickerModelCustomizer_WithOptionBuilder_UsesConfiguredSchema()
+    {
+        var optionBuilder = new TickerQEfCoreOptionBuilder<TimeTickerEntity, CronTickerEntity>();
+        optionBuilder.SetSchema("app_schema");
+
+        var services = new ServiceCollection();
+        services.AddSingleton(optionBuilder);
+        var serviceProvider = services.BuildServiceProvider();
+
+        var options = new DbContextOptionsBuilder<CustomAppDbContext>()
+            .UseSqlite(_connection)
+            .ReplaceService<IModelCustomizer, TickerModelCustomizer<TimeTickerEntity, CronTickerEntity>>()
+            .UseApplicationServiceProvider(serviceProvider)
+            .Options;
+
+        using var context = new CustomAppDbContext(options);
+        var model = context.Model;
+
+        var timeTickerEntity = model.FindEntityType(typeof(TimeTickerEntity));
+        Assert.NotNull(timeTickerEntity);
+        Assert.Equal("app_schema", timeTickerEntity.GetSchema());
+    }
+
+    #endregion
+}
+
+/// <summary>
+/// Simulates a user's application DbContext that uses UseApplicationDbContext path.
+/// </summary>
+public class CustomAppDbContext : DbContext
+{
+    public CustomAppDbContext(DbContextOptions<CustomAppDbContext> options) : base(options) { }
+}