diff --git a/src/EventSourcingTests/Bugs/Bug_2865_configuration_assertion_with_flat_table_projections.cs b/src/EventSourcingTests/Bugs/Bug_2865_configuration_assertion_with_flat_table_projections.cs
new file mode 100644
index 0000000000..e767c88700
--- /dev/null
+++ b/src/EventSourcingTests/Bugs/Bug_2865_configuration_assertion_with_flat_table_projections.cs
@@ -0,0 +1,114 @@
+using System;
+using System.Threading.Tasks;
+using Marten;
+using Marten.Events.Daemon.Resiliency;
+using Marten.Events.Projections;
+using Marten.Events.Projections.Flattened;
+using Marten.Testing.Harness;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Xunit;
+
+namespace EventSourcingTests.Bugs;
+
+public class Bug_2865_configuration_assertion_with_flat_table_projections
+{
+    [Fact]
+    public async Task should_be_able_to_assert_on_existence_of_flat_table_functions()
+    {
+        var appBuilder = Host.CreateApplicationBuilder();
+
+        appBuilder.Logging
+            .SetMinimumLevel(LogLevel.Information)
+            .AddFilter("Marten", LogLevel.Debug);
+
+        appBuilder.Services.AddMarten(options =>
+            {
+                options.Connection(ConnectionSource.ConnectionString);
+                options.DatabaseSchemaName = "flat_projections";
+
+                options.Projections.Add<FlatImportProjection>(ProjectionLifecycle.Async);
+            })
+            // Add this
+            .ApplyAllDatabaseChangesOnStartup()
+            .UseLightweightSessions()
+            .OptimizeArtifactWorkflow()
+            .AddAsyncDaemon(DaemonMode.Solo);
+
+        var app = appBuilder.Build();
+        await app.StartAsync();
+
+        var store = app.Services.GetRequiredService<IDocumentStore>();
+
+// ########## Uncomment the next line to get the error ##########
+        await store.Storage.Database.AssertDatabaseMatchesConfigurationAsync();
+
+        await using (var session = store.LightweightSession())
+        {
+            session.Events.StartStream(Guid.NewGuid(),
+                new ImportStarted(DateTimeOffset.Now.AddMinutes(-1), "foo", "cust-1", 3),
+                new ImportProgress("step-1", 3, 1),
+                new ImportFinished(DateTimeOffset.Now));
+
+            await session.SaveChangesAsync();
+        }
+
+        await app.StopAsync();
+    }
+}
+
+public record ImportStarted(DateTimeOffset Started, string ActivityType, string CustomerId, int PlannedSteps);
+public record ImportProgress(string StepName, int Records, int Invalids);
+public record ImportFinished(DateTimeOffset Finished);
+public record ImportFailed;
+
+public class FlatImportProjection : FlatTableProjection
+{
+    // I'm telling Marten to use the same database schema as the events from
+    // the Marten configuration in this application
+    public FlatImportProjection() : base("import_history", SchemaNameSource.EventSchema)
+    {
+        // We need to explicitly add a primary key
+        Table.AddColumn<Guid>("id").AsPrimaryKey();
+
+        TeardownDataOnRebuild = true;
+
+        Project<ImportStarted>(map =>
+        {
+            // Set values in the table from the event
+            map.Map(x => x.ActivityType, "activity_type").NotNull();
+            map.Map(x => x.CustomerId, "customer_id");
+            map.Map(x => x.PlannedSteps, "total_steps")
+                .DefaultValue(0);
+
+            map.Map(x => x.Started);
+
+            // Initial values
+            map.SetValue("status", "started");
+            map.SetValue("step_number", 0);
+            map.SetValue("records", 0);
+        });
+
+        Project<ImportProgress>(map =>
+        {
+            // Add 1 to this column when this event is encountered
+            map.Increment("step_number");
+
+            // Update a running sum of records progressed
+            // by the number of records on this event
+            map.Increment(x => x.Records);
+
+            map.SetValue("status", "working");
+        });
+
+        Project<ImportFinished>(map =>
+        {
+            map.Map(x => x.Finished);
+            map.SetValue("status", "completed");
+        });
+
+        // Just gonna delete the record of any failures
+        Delete<ImportFailed>();
+    }
+}
diff --git a/src/Marten/Events/Projections/Flattened/CallUpsertFunctionFrame.cs b/src/Marten/Events/Projections/Flattened/CallUpsertFunctionFrame.cs
index 44b9811927..16cceb6578 100644
--- a/src/Marten/Events/Projections/Flattened/CallUpsertFunctionFrame.cs
+++ b/src/Marten/Events/Projections/Flattened/CallUpsertFunctionFrame.cs
@@ -19,7 +19,7 @@ internal class CallUpsertFunctionFrame: MethodCall, IEventHandlingFrame
     public CallUpsertFunctionFrame(Type eventType, DbObjectName functionIdentifier, List<IColumnMap> columnMaps,
         MemberInfo[] members): base(typeof(IDocumentOperations), nameof(IDocumentOperations.QueueSqlCommand))
     {
-        _functionIdentifier = functionIdentifier;
+        _functionIdentifier = functionIdentifier ?? throw new ArgumentNullException(nameof(functionIdentifier));
         _columnMaps = columnMaps;
         _members = members;
         EventType = eventType;
diff --git a/src/Marten/Events/Projections/Flattened/FlatTableProjection.CodeGeneration.cs b/src/Marten/Events/Projections/Flattened/FlatTableProjection.CodeGeneration.cs
index 633d77c9dc..3ca28de9de 100644
--- a/src/Marten/Events/Projections/Flattened/FlatTableProjection.CodeGeneration.cs
+++ b/src/Marten/Events/Projections/Flattened/FlatTableProjection.CodeGeneration.cs
@@ -3,6 +3,7 @@
 using System.Reflection;
 using JasperFx.CodeGeneration;
 using JasperFx.Core;
+using JasperFx.Core.Reflection;
 using Marten.Events.CodeGeneration;
 
 namespace Marten.Events.Projections.Flattened;
diff --git a/src/Marten/Events/Projections/Flattened/StatementMap.cs b/src/Marten/Events/Projections/Flattened/StatementMap.cs
index 62e268d1a3..9e6c6687d0 100644
--- a/src/Marten/Events/Projections/Flattened/StatementMap.cs
+++ b/src/Marten/Events/Projections/Flattened/StatementMap.cs
@@ -30,6 +30,11 @@ public StatementMap(FlatTableProjection parent, MemberInfo[] pkMembers)
 
     IEventHandlingFrame IEventHandler.BuildFrame(EventGraph events, Table table)
     {
+        if (_functionIdentifier == null)
+        {
+            createFunctionName(table);
+        }
+
         return new CallUpsertFunctionFrame(typeof(T), _functionIdentifier, _columnMaps,
             determinePkMembers(events).ToArray());
     }
@@ -42,12 +47,17 @@ bool IEventHandler.AssertValid(EventGraph events, out string? message)
 
     IEnumerable<ISchemaObject> IEventHandler.BuildObjects(EventGraph events, Table table)
     {
-        var functionName = $"mt_upsert_{table.Identifier.Name}_{typeof(T).NameInCode().Sanitize()}";
-        _functionIdentifier = new PostgresqlObjectName(table.Identifier.Schema, functionName);
+        createFunctionName(table);
 
         yield return new FlatTableUpsertFunction(_functionIdentifier, table, _columnMaps);
     }
 
+    private void createFunctionName(Table table)
+    {
+        var functionName = $"mt_upsert_{table.Identifier.Name.ToLower()}_{typeof(T).NameInCode().ToLower().Sanitize()}";
+        _functionIdentifier = new PostgresqlObjectName(table.Identifier.Schema, functionName);
+    }
+
     private IEnumerable<MemberInfo> determinePkMembers(EventGraph events)
     {
         if (_pkMembers.Any())